Substrate temperature control in an ALD reactor

ABSTRACT

A deposition system includes a process chamber for conducting an ALD process to deposit layers on a substrate. An electrostatic chuck (ESC) retains the substrate. A backside gas increases thermal coupling between the substrate and the ESC. The ESC is cooled via a coolant flowing through a coolant plate and heated via a resistive heater. Various arrangements are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/000,825, entitled “Substrate Temperature Control In An ALD Reactor,”filed on Oct. 24, 2001 now abandoned, and incorporated herein byreference, which is a continuation-in-part of U.S. application Ser. No.09/902,080, entitled “Variable Gas Conductance Control For a ProcessChamber,” filed Jul. 9, 2001 now U.S. Pat. No. 6,800,173. These priorapplications claim priority from Provisional Application Ser. No.60/281,628, entitled “A Reactor For Atomic Layer Deposition,” filed Apr.5, 2001.

This application is also related to the following co-pendingapplications, which are incorporated herein by reference:

U.S. application Ser. No. 09/812,352, entitled “System And Method ForModulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19,2001.

U.S. application Ser. No. 09/812,486, entitled “Continuous Method ForDepositing A Film By Modulated Ion-Induced Atomic Layer Deposition(MII-ALD),” filed Mar. 19, 2001.

U.S. application Ser. No. 09/812,285, entitled “Sequential Method ForDepositing A Film By Modulated Ion-Induced Atomic Layer Deposition(MII-ALD),” filed Mar. 19, 2001.

U.S. application Ser. No. 09/854,092, entitled “Method And Apparatus forImproved Temperature Control In Atomic Layer Deposition,” filed May 10,2001.

U.S. Provisional Application Ser. No. 60/255,812, entitled “Method ForIntegrated In-Situ Cleaning And Subsequent Atomic Layer DepositionWithin A Single Processing Chamber,” filed Dec. 15, 2000.

FIELD OF THE INVENTION

The present invention relates to advanced thin film deposition apparatusand methods used in semiconductor processing and related technologies.

BACKGROUND

As integrated circuit (IC) dimensions shrink, the ability to depositconformal thin film layers with excellent step coverage at lowdeposition temperatures is becoming increasingly important. Thin filmlayers are used, for example, as MOSFET gate dielectrics, DRAM capacitordielectrics, adhesion promoting layers, diffusion barrier layers, andseed layers for subsequent deposition steps. Low temperature processingis desired, for example, to prevent unwanted diffusion of shallowjunctions, to better control certain reactions, and to preventdegradation of previously deposited materials and their interfaces.

The need for conformal thin film layers with excellent step coverage isespecially important for high aspect ratio trenches and vias, such asthose used in metallization layers of semiconductor chips. For example,copper interconnect technology requires a continuous thin film barrierlayer and a continuous thin film copper seed layer to coat the surfacesof trenches and vias patterned in an insulating dielectric prior tofilling the features with copper by electrochemical deposition (ECD orelectroplating).

A highly conformal, continuous barrier layer is required to preventcopper diffusion into the adjacent semiconductor (i.e., silicon)material or dielectric. The barrier layer also often acts as an adhesionlayer to promote adhesion between the dielectric and the copper seedlayer. Low dielectric constant (i.e., low-k) dielectrics are typicallyused to reduce inter- and intra-line capacitance and cross-talk, butoften suffer from poorer adhesion and lower thermal stability thantraditional oxide dielectrics, making the choice of a suitable adhesionlayer more critical. A non-conformal barrier layer, or one with poorstep coverage or discontinuous step coverage, can lead to copperdiffusion and current leakage between adjacent metal lines or todelamination at either the barrier-to-dielectric or barrier-to-seedlayer interfaces, both of which adversely affect product lifetime andperformance. The barrier layer should also be uniformly thin, to mostaccurately transfer the underlying trench and via sidewall profile tothe subsequent seed layer, and have a low film resistivity (e.g., ρ<500μΩ-cm) to lessen its impact on the overall conductance of the copperinterconnect structures.

A highly conformal, uniformly thin, continuous seed layer with lowdefect density is required to prevent void formation in the copperwires. The seed layer carries the plating current and acts as anucleation layer. Voids can form from discontinuities or other defectsin the seed layer, or they can form from pinch-off due to gross overhangof the seed layer at the top of features, both trenches and vias. Voidsadversely impact the resistance, electromigration, and reliability ofthe copper lines, which ultimately affects the product lifetime andperformance.

Traditional thin film deposition techniques, for example, physical vapordeposition (PVD) and chemical vapor deposition (CVD), are increasinglyunable to meet the requirements of advanced thin films. PVD, such assputtering, has been used for depositing conductive thin films at lowcost and at relatively low substrate temperature. Unfortunately, PVD isinherently a line of sight process, resulting in poor step coverage inhigh aspect ratio trenches and vias. Advances in PVD technology toaddress this issue have resulted in high cost, complexity, andreliability issues. CVD processes can be tailored to provide conformalfilms with improved step coverage. Unfortunately, CVD processes oftenrequire high processing temperatures, result in the incorporation ofhigh impurity concentrations, and have poor precursor (or reactant)utilization efficiency, leading to a high cost of ownership.

Atomic layer deposition (ALD), or atomic layer chemical vapor deposition(AL-CVD), is an alternative to traditional CVD methods to deposit verythin films. ALD has several advantages over PVD and traditional CVD. ALDcan be performed at comparatively lower temperatures (which iscompatible with the industry's trend toward lower temperatures), hashigh precursor utilization efficiency, can produce conformal thin filmlayers (i.e., 100% step coverage is theoretically possible), can controlfilm thickness on an atomic scale, and can be used to “nano-engineer”complex thin films.

A typical ALD process differs significantly from traditional CVDprocesses. In a typical CVD process, two or more reactant gases aremixed together in the deposition chamber where either they react in thegas phase and deposit on the substrate surface, or they react on thesubstrate surface directly. Deposition by CVD occurs for a specifiedlength of time, based on the desired thickness of the deposited film.Since this specified time is a function of the flux of reactants intothe chamber, the required time may vary from chamber to chamber.

In a typical ALD process deposition cycle, each reactant gas isintroduced sequentially into the chamber, so that no gas phaseintermixing occurs. A monolayer of a first reactant is physi- orchemisorbed onto the substrate surface. Excess first reactant is pumpedout, possibly with the aid of an inert purge gas. A second reactant isintroduced to the deposition chamber and reacts with the first reactantto form a monolayer of the desired thin film via a self-limiting surfacereaction. The self-limiting reaction halts once the initially adsorbedfirst reactant fully reacts with the second reactant. Excess secondreactant is pumped out, again possibly with the aid of an inert purgegas. A desired film thickness is obtained by repeating the depositioncycle as necessary. The film thickness can be controlled to atomic layer(i.e., angstrom scale) accuracy by simply counting the number ofdeposition cycles.

Physisorbed precursors are only weakly attached to the substrate.Chemisorption results in a stronger, more desirable bond. Chemisorptionoccurs when adsorbed precursor molecules chemically react with activesurface sites. Generally, chemisorption involves cleaving a weaklybonded ligand (a portion of the precursor) from the precursor, leavingan unsatisfied bond available for reaction with an active surface site.

The substrate material can influence chemisorption. In current dualdamascene copper interconnect structures, a barrier layer such astantalum (Ta) or tantalum nitride (TaN) must often simultaneously coversilicon dioxide (SiO₂), low-k dielectrics, nitride etch stops, and anyunderlying metals such as copper. Materials often exhibit differentchemical behavior, especially oxides versus metals. In addition, surfacecleanliness is important for proper chemisorption, since impurities canoccupy surface bonding sites. Incomplete chemisorption can lead toporous films, incomplete step coverage, poor adhesion between thedeposited films and the underlying substrate, and low film density.

The ALD process temperature must be selected carefully so that the firstreactant is sufficiently adsorbed (e.g., chemisorbed) on the substratesurface, and the deposition reaction occurs with adequate growth rateand film purity. A temperature that is too high can result in desorptionor decomposition (causing impurity incorporation) of the first reactant.A temperature that is too low may result in incomplete chemisorption ofthe first precursor, a slow or incomplete deposition reaction, nodeposition reaction, or poor film quality (e.g., high resistivity, lowdensity, poor adhesion, and/or high impurity content).

Traditional ALD processes have several disadvantages. First, since theprocess is entirely thermal, selection of an appropriate processtemperature is often confined to a narrow temperature window. Second,the small temperature window limits the selection of availableprecursors. Third, metal precursors that fit the temperature window areoften halides (e.g., compounds that include chlorine, flourine, orbromine), which are corrosive and can create reliability issues in metalinterconnects. Fourth, either gaseous hydrogen (H₂) or elemental zinc(Zn) is often used as the second reactant to act as a reducing agent tobring a metal compound in the first reactant to the desired oxidationstate of the final film. Unfortunately, H₂ is an inefficient reducingagent due to its chemical stability, and Zn has a low volatility and isgenerally incompatible with IC manufacturing. Thus, althoughconventional ALD reactors are suitable for elevated-temperature ALD,they limit the advancement of ALD processing technology.

Plasma-enhanced ALD, also called radical enhanced atomic layerdeposition (REALD), was proposed to address the temperature limitationsof traditional thermal ALD. For example, in U.S. Pat. No. 5,916,365, thesecond reactant passes through a radio frequency (RF) glow discharge, orplasma, to dissociate the second reactant and to form reactive radicalspecies to drive deposition reactions at lower process temperatures.More information on plasma-enhanced ALD is included in “Plasma-enhancedatomic layer deposition of Ta and Ti for interconnect diffusionbarriers,” by S. M. Rossnagel, et al., Journal of Vacuum Science andTechnology B 18(4) July/August 2000 pp. 2016-2020.

Plasma enhanced ALD, however, still has several disadvantages. First, itremains a thermal process similar to traditional ALD since the substratetemperature provides the required activation energy, and therefore theprimary control, for the deposition reaction. Second, althoughprocessing at lower temperatures is feasible, higher temperatures muststill be used to generate reasonable growth rates for acceptablethroughput. Such temperatures are still too high for some films ofinterest in IC manufacturing, particularly polymer-based low-kdielectrics that are stable up to temperatures of only 200° C. or less.Third, metal precursors, particularly for tantalum (Ta), often stillcontain chlorine as well as oxygen impurities, which results in lowdensity or porous films with poor barrier behavior and chemicalinstability. Fourth, the plasma enhanced ALD process, like theconventional sequential ALD process described above, is fundamentallyslow since it includes at least two reactant gases and at least twopurge or evacuation steps, which can take up to several minutes withconventional valve and chamber technology.

Conventional ALD reactors, including plasma enhanced ALD reactors,include a vertically-translatable pedestal to achieve a small processvolume, which is important for ALD. A small volume is more easily andquickly evacuated (e.g., of excess reactants) than a large volume,enabling fast switching of process gases. Also, less precursor is neededfor complete chemisorption during deposition. For example, the reactorsof U.S. Pat. No. 6,174,377 and European Patent No. 1,052,309 A2 featurea reduced process volume located above a larger substrate transfervolume. In practice, a typical transfer sequence includes transporting asubstrate into the transfer volume and placing it on top of a moveablepedestal. The pedestal is then elevated vertically to form the bottom ofthe process volume and thereby move the substrate into the processvolume. Thus, the moveable pedestal has at least a verticaltranslational and possibly a second rotational degree of freedom (forhigh temperature process uniformity).

Typical ALD reactors have significant disadvantages. First, conventionalALD reactors suffer from complex pedestal requirements, since thenumerous facilities (e.g., heater power lines, temperature monitorlines, and coolant channels) must be connected to and housed within apedestal that moves. Second, in the case of plasma enhanced ALD, theefficiency of radical delivery for deposition of conductive thin filmsis significantly decreased in downstream configurations in which theradical generating plasma is contained in a separate vessel remote fromthe main process chamber (see U.S. Pat. No. 5,916,365). Both gas phaseand wall recombinations reduce the flux of useful radicals to thesubstrate. In the case of atomic hydrogen (H), recombination results indiatomic H₂, a far less effective reducing agent. Other disadvantages ofknown ALD reactors exist.

Accordingly, improved ALD reactors are desirable to make ALD bettersuited for commercial IC manufacturing. Desirable characteristics ofsuch reactors might include higher throughput, improved deposited filmcharacteristics, better temperature control for narrow processtemperature windows, and wider processing windows (e.g., in particularwith respect to process temperature and reactant species).

SUMMARY

A deposition system in accordance with one embodiment of the presentinvention includes a process chamber for conducting an ALD process todeposit layers on a substrate. An electrostatic chuck (ESC) retains thesubstrate. A backside gas increases thermal coupling between thesubstrate and the ESC. The ESC is cooled via a coolant flowing through acoolant plate and heated via a resistive heater.

These and other aspects and features of the disclosed embodiments willbe better understood in view of the following detailed description ofthe exemplary embodiments and the drawings thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a novel ALD reactor.

FIG. 2 shows various embodiments of the shield and shadow ring overlapregion of FIG. 1.

FIG. 3 is a schematic diagram showing top introduction of gas into theprocess chamber of the ALD reactor of FIG. 1.

FIG. 4 is (a) a schematic diagram and (b) a plan view schematic diagramshowing side introduction of gas into the process chamber of the ALDreactor of FIG. 1.

FIG. 5 is (a) a schematic diagram and (b) a plan view schematic diagramshowing both top and side introduction of gas into the process chamberof the ALD reactor of FIG. 1.

FIG. 6 is a schematic diagram of a control system for the pedestal ofFIG. 1.

FIG. 7 is a schematic diagram of a circuit for electrical biasing of theelectrostatic chuck of FIG. 1.

FIG. 8 is a front-side perspective view of a novel ALD reactor.

FIG. 9 is a back-side perspective view of the ALD reactor of FIG. 8.

FIG. 10 is a back-side perspective view, from below, of the ALD reactorof FIG. 8.

FIG. 11 is a front-side cutaway perspective view of the ALD reactor ofFIG. 8.

FIG. 12 is a front-side cutaway perspective view of the ALD reactor ofFIG. 8.

FIG. 13 is a cross-sectional view of a chamber portion of the ALDreactor along line 13-13 of FIG. 8.

FIG. 14 is a detailed cross-sectional view of the right side of thechamber portion of FIG. 13 showing a load shield position.

FIG. 15 is a detailed cross-sectional view of the right side of thechamber portion of FIG. 13 showing a low conductance process shieldposition.

FIG. 16 is a detailed cross-sectional view of the right side of thechamber portion of FIG. 13 showing a high conductance process shieldposition.

FIG. 17 is a detailed cross-sectional view of the right side of thechamber portion of FIG. 13 showing a purge shield position.

FIG. 18 is a schematic diagram of a valve system for gas delivery in theALD reactor of FIG. 8.

FIG. 19 is a schematic diagram of a valve system for gas delivery in theALD reactor of FIG. 8.

FIG. 20 is a schematic diagram of a valve system for gas delivery in theALD reactor of FIG. 8.

FIG. 21 is a schematic diagram of a valve system for gas delivery in theALD reactor of FIG. 8

FIG. 22 is a schematic diagram of a valve system for gas delivery in theALD reactor of FIG. 8.

FIG. 23 is a perspective cross-section of two embodiments of ashowerhead for gas distribution.

FIG. 24 is a perspective cross-section of an embodiment of a shieldassembly for the ALD reactor of FIG. 8.

FIG. 25 is a perspective cross-section of an embodiment of a shieldassembly for the ALD reactor of FIG. 8.

FIG. 26 is a perspective cross-section of an embodiment of a shieldassembly for the ALD reactor of FIG. 8.

FIG. 27 is a cutaway perspective view of an embodiment of anelectrostatic chuck assembly for the ALD reactor of FIG. 8.

FIG. 28 is a schematic diagram of a control system for the electrostaticchuck assembly of FIG. 27 of the ALD reactor of FIG. 8.

FIG. 29 is a schematic diagram of a control system including analternative energy source for the electrostatic chuck assembly of FIG.27 of the ALD reactor of FIG. 8.

FIG. 30 is a perspective view of an embodiment of a portion of anelectrostatic chuck assembly for the ALD reactor of FIG. 8.

FIG. 31 is a schematic diagram of a circuit for electrical biasing ofthe electrostatic chuck of the ALD reactor of FIG. 8.

FIG. 32 is a schematic diagram of a circuit for electrical biasing ofthe electrostatic chuck of the ALD reactor of FIG. 8.

FIG. 33 is a schematic diagram of a circuit for electrical biasing ofthe electrostatic chuck of the ALD reactor of FIG. 8.

FIG. 34 is a schematic illustration of a conventional ALD process.

FIG. 35 is a schematic illustration of a novel ALD process.

FIG. 36 shows timing diagrams for (a) a typical prior art ALD processand (b) a novel ALD process.

FIG. 37 shows timing diagrams for an alternative embodiment of a novelALD process.

FIG. 38 shows timing diagrams for an alternative embodiment of a novelALD process.

FIG. 39 is a schematic illustration of a novel chemisorption techniquefor ALD processes.

FIG. 40 is a schematic diagram of a circuit for electrical biasing ofthe electrostatic chuck of the ALD reactor of FIG. 8 for improvedchemisorption.

In the drawings, like or similar features are typically labeled with thesame reference numbers.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Basic ALD Reactor Design

FIG. 1 is a schematic diagram of a novel ALD reactor 2. Reactor 2includes a stationary pedestal 4, which may include an electrostaticchuck (ESC) 6 on top of which a substrate 8 rests. Substrate 8 isusually a semiconductor wafer (e.g., silicon), but may be a metallizedglass substrate or other substrate. A chamber lid 10 and ESC 6 definethe top and bottom boundaries, respectively, of a process chamber 12.The surrounding wall of chamber 12 is defined by a moveable shield 14,which is attached to a plurality of shield support legs 16. The volumeof process chamber 12 is smaller than prior art batch reactors, but maybe similar in size to prior art single wafer systems. The configurationof reactor 2, however, provides an overall volume of reactor 2 that canbe smaller than that of prior art reactors, while providing the smallvolume of process chamber 12.

The small volume of process chamber 12 achieves the advantages of smallprocess volumes discussed above, including quick evacuation, fastswitching of process gases, and less precursor required for completechemisorption. The volume of process chamber 12 cannot be madearbitrarily small, however, since substrate 8 must still be transferredinto, and out of, process chamber 12.

In FIG. 1, the fixed position of pedestal 4, including its supportinghardware, simplifies overall design of reactor 2, allowing ease of useand maintenance as well as improved performance. In comparison tomassive moveable pedestals in prior art reactors, shield 14 includesless associated hardware and is much lighter, which allows precisionpositioning of shield 14 to adjust the conductance of, and facilitatepumping of, chamber 12 with rapid response.

A chamber body 18 surrounds shield 14, chamber lid 10, and pedestal 4(including ESC 6), defining an annular pumping channel 20 exterior toshield 14. During processing, shield 14 separates process chamber 12, atlow pressure, from annular pumping channel 20, which is maintained at alower pressure than the chamber to maintain a clean background ambientin reactor 2. The volume of chamber 12 is coupled to annular pumpingchannel 20 via a shield conductance upper path 22 and a shieldconductance lower path 24. Upper path 22 and lower path 24 are eachdefined by portions of shield 14 and corresponding features ofstationary components of reactor 2. In the embodiment shown in FIG. 1,upper path 22, typically a variable low leakage path during processing,is bounded by an inner wall of shield 14 and chamber lid 10. Lower path24, a variable high leakage path through a shield and shadow ringoverlap region 26, is bounded by a portion of shield 14 and a shadowring 28. Shadow ring 28 is actually separate from ESC 6 and is shown ingreater detail in subsequent figures.

The structures of shield 14 and shadow ring 28 may vary to providedifferent conductances of lower path 24 as shown in FIG. 2, which showsvarious embodiments of the shield and shadow ring overlap region 26 ofFIG. 1. The conductance of a flow path is related to the length of therestriction as well as the physical dimensions of the path. For example,a shorter path with a large cross-sectional area has a higherconductance. For the embodiments shown in FIG. 2, the structuralconfigurations of shield 14 and shadow ring 28 result in a highestconductance path 30, a second highest conductance path 32, a thirdhighest conductance path 34, and a lowest conductance path 36.Practitioners in the art will appreciate that many other embodiments ofshield and shadow ring overlap region 26 are possible.

Various shield positions are employed throughout a novel ALD process.Raising shield 14 to its highest position (along with shadow ring 28)allows for introduction or removal of substrate 8. Dropping shield 14 toits lowest position allows rapid evacuation of chamber 12 via upper path22 by exposure to the vacuum of annular pumping region 20. Shield 14 ispositioned at intermediate positions during processing depending on gasdelivery and conductance requirements.

The motion of shield 14 can be used to precisely control the spatialrelationship between shield 14 and shadow ring 28, thereby providing atunable conductance for chamber 12 primarily via lower path 24. Thisallows quick, precise control of the pressure in chamber 12, even duringprocessing, which is not possible in prior art methods that employ amoveable pedestal since vertical motion of substrate 8 is undesirableduring processing. The tunable conductance also allows quick, precisecontrol of the residence time of gases introduced to chamber 12 formultiple flow rates, and it allows minimal waste of process gases.

Basic Gas Introduction to an ALD Reactor

Reactor 2 of FIG. 1 supports gas introduction through multiple points,including top introduction, side introduction, or a combination of bothtop and side introductions.

FIG. 3 is a schematic diagram showing top introduction of gas intoprocess chamber 12 of ALD reactor 2 of FIG. 1. A top mount feed (notshown) has a single introduction point (or multiple introduction points)with an optional added device (not shown), such as a showerhead and/or abaffle, to ensure that a top introduction flow distribution 38 isuniform over the substrate. The added device includes at least onepassage, and may include many. The added device may also includeintermediate passages to regulate gas distribution and velocity.

FIG. 4 is (a) a schematic diagram and (b) a plan view schematic diagramshowing side introduction of gas into process chamber 12 of ALD reactor2 of FIG. 1. Gas is introduced from a gas channel 40 in shield 14 intoprocess chamber 12 through orifices in an inner wall of shield 14. Gasis introduced in a symmetric geometry around substrate 8 designed toensure that a side introduction flow distribution 42 is even. Inaddition, the plane of the gas introduction may be adjusted verticallyrelative to substrate 8 before or during gas introduction, which can beused to optimize flow distribution 42.

FIG. 5 is (a) a schematic diagram and (b) a plan view schematic diagramshowing both top and side introduction of gas into process chamber 12 ofALD reactor 2 of FIG. 1. The gases for novel ALD processes, includingprecursor and purge gases, can be introduced through the sameintroduction path or separate paths as desired for optimal performanceand layer quality.

Basic Electrostatic Chuck Assembly Design for an ALD Reactor

Reactor 2 of FIG. 1 can be used in a deposition process where theactivation energy for the surface reaction is provided by ions createdin a plasma above the substrate. Thus, atomic layer deposition can beion-induced, rather than thermally induced. This allows deposition atmuch lower temperatures than conventional ALD systems. Given thesufficiently low process temperatures, pedestal 4 may include anelectrostatic chuck (ESC) 6 for improved temperature control andimproved radio frequency (RF) power coupling.

Additional detail of ion-induced atomic layer deposition may be found inthe following related applications. U.S. application Ser. No.09/812,352, entitled “System And Method For Modulated Ion-Induced AtomicLayer Deposition (MII-ALD),” filed Mar. 19, 2001, assigned to thepresent assignee and incorporated herein by reference. U.S. applicationSer. No. 09/812,486, entitled “Continuous Method For Depositing A FilmBy Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar.19, 2001, assigned to the present assignee and incorporated herein byreference. U.S. application Ser. No. 09/812,285, entitled “SequentialMethod For Depositing A Film By Modulated Ion-Induced Atomic LayerDeposition (MII-ALD),” filed Mar. 19, 2001, assigned to the presentassignee and incorporated herein by reference.

FIG. 6 is a schematic diagram of a control system 44 for pedestal 4 ofFIG. 1. Substrate 8 rests on an annular sealing lip 46 defining abackside gas volume 48 between substrate 8 and a top surface 50 of ESC 6of pedestal 4. The backside gas flows from a backside gas source 52along a backside gas line 54, through a backside gas passageway 56 inESC 6, and into gas volume 48. The backside gas improves the thermalcommunication between substrate 8 and ESC 6 by providing a medium forthermal energy transfer between substrate 8 and ESC 6. A means of flowcontrol, such as a pressure controller 58, maintains the backside gas ata constant pressure, thus ensuring a uniform substrate temperature.

Substrate temperature is modulated by heating or cooling ESC 6. Atemperature sensor 60 is coupled via a sensor connection 62 to atemperature monitor 64. A temperature controller 66 controls a heaterpower supply 68 applied via an electrical connection 70 to a resistiveheater 72 embedded in ESC 6. A coolant temperature and flow controller74, as is widely known, controls the coolant from a coolant supply 76 asit flows in a plurality of coolant channels 78 in pedestal 4.

ESC 6 includes at least a first electrode 80 and a second electrode 82embedded in a dielectric material. FIG. 7 is a schematic diagram of acircuit 84 for electrical biasing of electrostatic chuck 6 of pedestal 4of FIG. 1. First electrode 80 and second electrode 82 are biased withdifferent DC potentials to provide the “chucking” action that holdssubstrate 8 (FIG. 1) to ESC 6 prior to plasma ignition and duringdeposition. The biasing scheme of FIG. 7 allows establishment of theelectrostatic attraction (i.e., “chucking”) at low biases that would beinsufficient to generate enough electrostatic attraction with aconventional monopolar chuck. In FIG. 7, one terminal of a DC powersupply 86 is coupled via a first inductor 88 to first electrode 80. Theother terminal of DC power supply 86 is coupled via a second inductor 90to second electrode 82. Inductors 88 and 90 serve as RF filters.

RF power (e.g., at 13.56 MHz) is also supplied simultaneously to bothfirst electrode 80 and second electrode 82 using an RF generator 92coupled to a ground terminal 94. A first capacitor 96 and a secondcapacitor 98 are respectively coupled between RF generator 92 and firstelectrode 80 and second electrode 82. Capacitors 96 and 98 serve as DCfilters to block the DC voltage from power supply 86. Circuit 84 allowsimproved coupling of RF power to substrate 8 during processing due tothe close proximity (e.g., 0.6 mm-2 mm spacing) of substrate 8 to firstelectrode 80 and second electrode 82 embedded in ESC 6.

Since substrate 8 is in such close proximity to first and secondelectrodes 80 and 82, the transmission efficiency of RF power throughthe intervening dielectric of ESC 6 is higher than in conventionalreactors where RF power is applied to electrodes at a greater distancefrom the substrate. Thus, less power is needed to achieve sufficient RFpower coupling to substrate 8 in novel ALD reactor 2 (FIG. 1), and thesame power to generate the bias on substrate 8 can also be used tocreate a plasma above substrate 8 at very low powers (e.g., <600 W, andtypically <150 W).

ALD Reactor Detail

FIG. 8, FIG. 9, FIG. 10, FIG. 11, and FIG. 12 show external views andinternal cutaway views of a novel ALD reactor 100. FIG. 8 is afront-side perspective view of reactor 100. FIG. 9 is a back-sideperspective view of reactor 100. FIG. 10 is a back-side perspectiveview, from below, of reactor 100. FIG. 11 is a front-side cutawayperspective view of reactor 100. FIG. 12 is another front-side cutawayperspective view of reactor 100.

Referring to FIG. 8, a substrate 8 (FIG. 12) is transferred into or outof a process chamber 12 (FIG. 11 and FIG. 12) of reactor 100 through asubstrate entry slot 102 in a slit valve 104. Substrate 8 is loaded ontoor unloaded from the pedestal (e.g., an electrostatic chuck assembly 106as seen in FIG. 11 and FIG. 12) by a plurality of lift pins 108. In theload or unload position, the tips of lift pins 108 extend throughorifices in an electrostatic chuck (ESC) 6 to hold substrate 8 above thetop surface of ESC 6. In the process position, the tips of lift pins 108retract below the top surface of ESC 6 allowing contact betweensubstrate 8 and ESC 6 (FIG. 11 and FIG. 12).

Referring to FIG. 11 and FIG. 12, lift pins 108 extend downward fromprocess chamber 12 in the interior of reactor 100 through anelectrostatic chuck assembly 106 (including ESC 6, a cooling plate 110,and a baseplate 112) to the exterior under-side of reactor 100. Each oflift pins 108 is attached to a lift pin spider 114 to coordinate theirmotion. Vertical translation of lift pin spider 114 is accomplished withan off-axis lift pin actuator 116 (e.g., a pneumatic cylinder), whichcontrols motion of a tie rod 118 that is coupled to lift pin spider 114by a spherical joint 120 as seen in FIG. 10. Spherical joint 120transmits lifting forces to lift pin spider 114 but no moments.

Referring to FIG. 11, to facilitate substrate transfer, a moveableshield 14, must be in a load position. Shield 14 is raised or loweredusing a linear motor 122, which moves a linear motor output rod 124attached to a shield lift spider 126 by a collet clamp 128 (best seen inFIG. 10). Each one of a plurality of shield support legs 16 (FIG. 11)extends through a shield support leg seal 130 and is coupled betweenshield lift spider 126 and shield 14. The axis of linear motor 122 isaligned with the axis of process chamber 12 resulting in no net momentson shield lift spider 126. Lift pin spider 114 rides a portion of linearmotor output rod 124, coaxial with output rod 124 and shield lift spider126. Lift pin spider 114, however, is unaffected by movement of rod 124,and this arrangement results in no net moments on lift pins 108.

As mentioned above, linear motor 122 provides actuation of shield 14.This is in contrast to conventional moveable pedestals wherein slowerstepper motors are used for actuation. Conventional rotational steppermotors use lead screws (possibly in conjunction with a gear train),which are slow but capable of moving heavy masses, to effect movement ofthe heavy pedestal. Linear motor 122 does not use a gear train, butinstead directly drives the load. Linear motor 122 includes a pluralityof alternating magnets to effect motion of output rod 124.

Linear motor 122 can be a commercially available linear motor andtypically includes a sleeve having a coil and a moveable rod enclosingthe series of alternating magnets. The movement of the rod through thesleeve is precisely controlled, using a Hall Effect magnetic sensor, bya signal applied to the coil. In one embodiment, pulses applied to thecoil precisely control the position of the rod with respect to thesleeve, as is well known. Since shield 14 is a light weight compared toconventional heavy pedestals, linear motor 122 provides high performancepositioning, with response times on the order of milliseconds. Linearmotor 122 thus provides a quicker response and more accurate shieldpositioning than is achievable with conventional stepper or servo motorsused to actuate the pedestal of conventional ALD reactors.

Referring to FIG. 11, a pump, such as a turbomolecular pump 132,maintains a background ambient pressure as low as a few microtorr orless in an annular pumping channel 20 surrounding shield 14. Pump 132 isattached to reactor 100 at an angle such that a circular pump throat 134is fully exposed to a narrow pumping slot 136 aft of process chamber 12,maximizing the conductance between them. In this manner, pump 132 with adiameter, d, has maximum exposure to pumping slot 136 of height, h(where h<d), with minimum restriction between pump 132 and chamber 12(see also FIG. 13 discussed below). For specific processingapplications, a pumping speed restrictor 138 can be inserted at pumpthroat 134 to restrict the conductance as needed. In some embodiments, apressure controlling throttle valve (e.g., a butterfly valve) can beused instead of, or in conjunction with, restrictor 138. Pressure inpumping slot 136 and annular pumping channel 20 is monitored by a pumppressure sensor 140 mounted on the top surface of reactor 100.

Process chamber 12 is bounded on top by a chamber lid 10. Pressure inprocess chamber 12 of reactor 100 may be on the order of a few microtorrup to several torr. The pressure of chamber 12 is monitored by a fastchamber pressure sensor 142 and a precision chamber pressure sensor 144,both of which are mounted on an upper peripheral flange of chamber lid10 (FIG. 8). The temperature of chamber lid 10 is controlled by fluidflowing in a plurality of lid cooling/heating channels 146 (FIG. 11).One possible path of gas introduction to process chamber 12 is through ashowerhead three-way valve 148 mounted centrally on chamber lid 10.Another possible method of gas introduction to process chamber 12 isthrough a shield gas channel 40.

RF power is transferred to electrodes in ESC 6 via an RF conductor 150shielded within an RF insulator tube 152. A gas medium (commonlyreferred to as a backside gas) is provided via a backside gas valve 154to ESC 6 to improve the thermal coupling between ESC 6 and substrate 8.During processing, an optional shadow ring 28 rests on a portion of ESC6 fully surrounding a peripheral edge of substrate 8.

FIG. 13 is a cross-sectional view of a chamber portion 156 of ALDreactor 100 along line 13-13 of FIG. 8. Substrate entry slot 102 isshown on the left hand side extending through a chamber body 18. Pumpingslot 136, of height h, is shown on the right hand side extending throughchamber body 18 to pump throat 134, of diameter d. The temperature ofchamber body 18 is controlled by fluid flowing in a chambercooling/heating channel 158.

Chamber lid 10 rests atop chamber body 18. A vacuum seal, to maintainlow pressure in the interior of reactor 100, is maintained through theuse of an upper O-ring 160 between chamber lid 10 and chamber body 18.Laterally spaced from O-ring 160 between chamber lid 10 and chamber body18 is an upper RF gasket 162, forming an RF shield. The temperature ofchamber lid 10 is controlled by fluid flowing in lid cooling/heatingchannels 146. Alternatively, the temperature of chamber lid 10 may becontrolled by an electric or resistive heater or other cooling/heatingmeans.

The pressure in process chamber 12 is monitored, in part, by fastchamber pressure sensor 142, which is mounted on an upper peripheralflange of chamber lid 10. Pressure sensor 142 monitors the pressure in apressure tap volume 164, which is coupled to process chamber 12 by apressure sensor orifice 166. This arrangement allows exposure ofpressure sensor 142 to the pressure of chamber 12, while preventingplasma and other process chemistries from reaching, and possiblydamaging, pressure sensor 142.

Gases can be introduced into process chamber 12 through a showerhead gasfeed inlet 168, which leads to a plenum 170 above a showerhead 172attached to a lower surface of chamber lid 10. Showerhead 172 includes ashowerhead lip 174 and a plurality of showerhead gas orifices 176, whichare used to distribute gas evenly into process chamber 12.

Substrate 8 rests on an upper surface of an ESC assembly 106, whichincludes in part, ESC 6, cooling plate 110, and baseplate 112. Thevertical spacing between the upper surface of ESC assembly 106 andshowerhead 172 may be 0.3 inches to 1 inch, typically less than 0.6inches. Backside gas passageway 56 is shown centrally located in andextending through ESC 6. ESC 6, which includes the largest portion ofthe upper surface on which substrate 8 rests, is held in contact withcooling plate 110 using a clamp ring 178, which overlaps a surroundingflange at the base of ESC 6. A plurality of clamp ring fasteners 180,each extending through clamp ring 178 into cooling plate 110, secure theconnection between ESC 6 and cooling plate 110. A process kit 182 fullysurrounds clamp ring 178 and electrically hides clamp ring fasteners 180from ESC 6 and substrate 8. For a more detailed view of clamp ring 178,fasteners 180, and process kit 182, see FIG. 16, discussed below.

The temperature of cooling plate 10 is controlled using fluid flowing ina plurality of coolant channels 78 as shown in FIG. 13. An upper surfaceof cooling plate 110 is patterned to create a plurality of thermalbreaks 184, or gaps, between ESC 6 and cooling plate 10. Thermal breaks184 increase the temperature difference between ESC 6 and cooling plate110. This allows the temperature of ESC 6 to rise substantially higherthan the temperature of baseplate 112, which stays relatively cool. Fora more detailed view of thermal breaks 184, see FIG. 27, discussedbelow.

As shown in FIG. 13, a lower surface of cooling plate 10 is attached toan upper surface of baseplate 112. The upper surface of baseplate 112forms the lower walls of coolant channels 78 in cooling plate 10. Avacuum seal, to maintain low pressure in the interior of reactor 100, ismaintained through the use of an O-ring 186 between baseplate 112 andchamber body 18. Laterally spaced from O-ring 186 between baseplate 112and chamber body 18 is an RF gasket 188.

One of the plurality of lift pins 108 is shown in retracted processposition, with the tip of lift pin 108 below the top surface of ESC 6.Lift pin 108 extends through a lift pin seal 190, which maintains thelow pressure in the interior of reactor 100. A lift pin bushing 192reduces friction during vertical translation of lift pin 108 throughaligned orifices in baseplate 12, cooling plate 10, and ESC 6.

In FIG. 13, shield 14 is shown in an intermediate process position.Process chamber 12 is thus bounded on the top by showerhead 172, on thebottom largely by ESC 6, and on the sides by shield 14 to confine aplasma 194. Shield 14 includes shield gas channel 40 and is attached toeach shield support leg 16 using a shield cap 196. Each shield supportleg 16 extends through shield support leg seal 130, which maintains thelow pressure in the interior of reactor 100. A plurality of shieldsupport leg bushings 198 reduce friction during vertical translation ofshield support legs 16 through orifices in baseplate 112.

A shadow ring hook 200 is attached to a lower portion of shield cap 196.Shadow ring hook 200 is shown interdigitated with shadow ring 28, whichfully surrounds a peripheral edge of ESC assembly 106 and rests on aprocess kit bevel 202 of process kit 182. Shadow ring 28 protects theunderlying portions of ESC assembly 106 during deposition onto substrate8. Shadow ring 28 also defines the circumferential region near the edgeof substrate 8 where deposition is masked. Shadow ring 28 also plays arole in defining the chamber conductance. For a more detailed view ofprocess kit bevel 202, see FIG. 16, discussed below.

In FIG. 13, two leakage paths modulate gas flow between process chamber12 and annular pumping channel 20, which is largely bounded by chamberbody 18, chamber lid 10, and ESC assembly 106. The leakage occurs due todiffering pressures between process chamber 12 and annular pumpingchannel 20. A shield conductance upper path 22 is bounded on one side byan inner upper surface of shield 14, and on the other side by outersurfaces of chamber lid 10 and showerhead 172. A shield conductancelower path 24 is bounded on one side by surfaces of a lower portion ofshield 14, shield cap 196, and shadow ring hook 200, and on the otherside by surfaces of shadow ring 28. Upper path 22 leads from processchamber 12 to an upper portion 204 of annular pumping channel 20, whilelower path 24 leads from process chamber 12 to a lower portion 206 ofannular pumping channel 20.

Shield 14 can be vertically translated by either raising it into upperportion 204 of annular pumping channel 20 or lowering it into lowerportion 206 of annular pumping channel 20. As shield 14 is translated,the conductances of upper path 22 and lower path 24 are changed. Thevariations in conductance can be controlled to vary the pressure inprocess chamber 12 in a controlled manner as needed for various steps inan atomic layer deposition process sequence.

Shield Operation

Unlike in conventional ALD reactors, reactor 2 includes a stationarypedestal 4 (see FIG. 1). For example, reactor 100 of FIG. 12 includesESC assembly 106. Transfer of substrate 8 into process chamber 12 ofreactor 100 is facilitated through the use of moveable shield 14, whichalso plays a significant role during processing.

Various shield positions are employed throughout the ALD process. FIG.14, FIG. 15, FIG. 16, and FIG. 17 show detailed cross-sectional views ofthe right side of chamber portion 156 of FIG. 13, showing shield 14 in asubstrate load shield position 208 (FIG. 14), a low conductance processshield position 210 (FIG. 15), a high conductance process shieldposition 212 (FIG. 16), and a purge shield position 214 (FIG. 17).

In load shield position 208 of FIG. 14, shield support legs 16 areraised by linear motor 122 (FIG. 8). When shield 14 is raised above acertain point, shadow ring hook 200 contacts shadow ring 28 and lifts itas well. Shield 14 and shadow ring 28 are then raised together. Shield14 enters upper portion 204 of annular pumping channel 20. Shield 14 andshadow ring 28 can be raised until shadow ring 28 contacts showerheadlip 174, which prevents shadow ring 28 from contacting showerhead 172.

Load shield position 208 thus allows loading (or unloading) of substrate8 into (or out of) process chamber 12 via substrate entry slot 102 (FIG.13). For example, to load substrate 8 into process chamber 12, asubstrate blade or paddle (not shown) carries substrate 8 into processchamber 12. Lift pins 108 are raised by lift pin actuator 116 (FIG. 10)to contact substrate 8 and lift it off the top surface of the blade. Theblade is then retracted out of chamber 12 through entry slot 102. Liftpins 108 are retracted past the top surface of ESC 6 allowing substrate8 to rest on ESC 6 as shown in FIG. 14. A similar process is followed tounload substrate 8 from chamber 12.

In an alternative embodiment, shadow ring 28 is not used, and shield 14forms variable conduction paths with other surfaces that may be fixed ormoveable. In some embodiments, it is possible that the load position maybe achieved by lowering shield 14 sufficiently so that substrate 8 maypass over the top edge of shield 14.

Once substrate 8 has been loaded into process chamber 12, shield 14 islowered by linear motor 122 (FIG. 8) for processing. The low conductanceprocess shield position 210 shown in FIG. 15, shows the positions ofshield 14 and shadow ring 28 at the moment that shadow ring 28 contactsprocess kit 182. An angled shadow ring seat 216 of shadow ring 28 restson process kit bevel 202 of process kit 182. This is the only point ofcontact between shadow ring 28 and process kit 182. Air gaps separateshadow ring 28 and process kit 182 away from each edge of process kitbevel 202. The airgaps between shadow ring 28 and process kit 182 allowfor differential thermal expansion of shadow ring 28 and process kit 182during processing. The angle of process kit bevel 202 helps centershadow ring 28, through interaction with the angle of shadow ring seat216, so that the edge of substrate 8 is shadowed uniformly by a shadowring edge 218 of shadow ring 28.

Lowering shield 14 into process position creates shield conductanceupper path 22 and shield conductance lower path 24, as described withrespect to FIG. 13 above. While it is possible to reduce the conductanceof lower path 24 to zero (FIG. 15), during deposition upper path 22generally forms a low conductance leakage path, while lower path 24generally forms a higher conductance leakage path (FIG. 16).

By changing the relative position of shield 14 to shadow ring 28, theconductance out of chamber 12 can be modulated. This modulation, inturn, alters the pressure of chamber 12. The high conductance processshield position 212 shown in FIG. 16, shows the positions of shield 14and shadow ring 28 at an intermediate step of an ALD process. Lower path24 includes several distinct regions: a plurality (three in thisembodiment) of fixed conductance regions 220 (fixed gaps between shadowring hook 200 and shadow ring 28) interspersed with a plurality (two inthis embodiment) of variable conductance regions 222 (variable gaps).The volumes of fixed conductance regions 220 and variable conductanceregions 222 can be precisely controlled (by precise positioning ofshield 14 by linear motor 122) to adjust the conductance of lower path24, and therefore the pressure of chamber 12, as needed during theprocess.

In purge shield position 214 of FIG. 17, shield support legs 16 arelowered by linear motor 122 (FIG. 8). Shield 14 and shadow ring hook 200are lowered into lower portion 206 of annular pumping channel 20. Shadowring 28 remains seated on process kit 182. Both shield conductance upperpath 22 and shield conductance lower path 24 become high conductancepaths. Purge shield position 214 allows quick evacuation of the gases inprocess chamber 12 into annular pumping channel 20 due to the highconductances created and the lower pressure of annular pumping channel20 compared to chamber 12.

As mentioned above, linear motor 122 (FIG. 8) provides actuation ofshield 14. This allows quick and accurate variation of the conductanceof shield conductance upper and lower paths 22 and 24. This translatesinto quick and accurate variation of the pressure in process chamber 12for given gas flows into process chamber 12.

In some embodiments, a throttle valve (i.e., a butterfly valve, avariable position gate valve, a pendulum valve, etc.) positioned at pumpthroat 134 (FIG. 13) can also be used in conjunction with moveableshield 14 to effect quick pressure changes in process chamber 12 bymodulating the maximum pumping speed of pump 132 (FIG. 12). The throttlevalve augments the pressure range achievable in process chamber 12,providing a “coarse adjustment” of the pressure in process chamber 12,while shield 14 provides a “fine adjustment” of the pressure.

Showerhead and Shield Design for Gas Introduction and TemperatureControl

The novel hardware for ALD reactor 100 (FIG. 11) supports theintroduction of gases into process chamber 12 through multiple points.The primary introduction point is through the top of reactor 100, inparticular, through showerhead three-way valve 148 (mounted on chamberlid 10) and showerhead 172 (best seen in FIG. 13). Gases may also beintroduced into chamber 12 through shield 14, which may be additionallyconfigured for temperature control.

FIG. 18 is a schematic diagram of a novel valve system 224 for gasdelivery in ALD reactor 100 of FIG. 8. This embodiment delivers a singleprecursor and a purge gas to process chamber 12, either separately or ina mixed proportion. The purge gas is used to purge the chamber and asthe gas source to strike a plasma. A carrier gas for the precursor flowsfrom a first gas source 226, and the purge gas flows from a second gassource 228.

When either the carrier gas or the purge gas is not flowing to chamber12, it is diverted by a first three-way valve 230 and a purge three-wayvalve 232, respectively, through a pump bypass gas line 234 to a vacuumpump 236. Utilization of vacuum pump 236 allows the carrier and purgegases to flow in steady state conditions even when they are not flowingto chamber 12. This avoids disturbances in the gas flows caused by thelong settling times of gas sources that are switched on and off.

A showerhead three-way valve 148 controls access to a chamber gas line238, which leads to process chamber 12. Three-way valve 148, locatedcentrally on chamber lid 10 as seen in FIG. 11, provides at least twodistinct advantages. First, gases introduced to chamber 12 can beswitched rapidly with minimal loss or delay. Second, gases are isolatedfrom each other outside of chamber 12, resulting in nocross-contamination of reactants.

A first on/off valve 240 is coupled between first ends of a secondon/off valve 242 and a third on/off valve 244. The opposite ends ofsecond and third on/off valves 242 and 244 are each coupled to a firstprecursor source 246. First on/off valve 240 is also coupled betweenfirst three-way valve 230 and showerhead three-way valve 148 via a gasline 248 and a gas line 250, respectively. Precursor source 246 can beisolated by closing on/off valves 242 and 244. This may be done, forexample, to change precursor source 246. In this case, on/off valve 240may be closed, or opened to allow carrier gas to flow through three-wayvalves 230 and 148 into chamber 12. During deposition, first on/offvalve 240 is normally closed, and second and third on/off valves 242 and244 are normally open.

Three-way valves 230, 232, and 148 are switched synchronously to delivereither precursor or purge gas to chamber 12. When delivering precursor,purge three-way valve 232 is switched to flow the purge gas to vacuumpump 236, and showerhead three-way valve 148 is switched to theprecursor side. Simultaneously, three-way valve 230 is switched to allowcarrier gas to flow from first gas source 226 through gas line 248 andon/off valve 242 into precursor source 246. The carrier gas picks upprecursor in precursor source 246, typically by bubbling through aliquid source. The carrier gas, now including precursor, flows throughon/off valve 244, through gas line 250, through showerhead three-wayvalve 148, through chamber gas line 238, and into chamber 12.

When delivering purge gas, first three-way valve 230 is switched to flowthe carrier gas to vacuum pump 236. Purge three-way valve 232 andshowerhead three-way valve 148 are switched to allow purge gas to flowfrom second gas source 228 through a gas line 252 and chamber gas line238 into chamber 12.

Valve system 224 keeps gas line 248 charged with carrier gas, gas line250 charged with carrier plus precursor, and gas line 252 charged withpurge gas. This allows fast switching between gas sources bysignificantly reducing the gas delivery time to chamber 12. Valve system224 also minimizes waste of gases since gas lines do not need to beflushed between deposition steps. Furthermore, any gas bursts fromtransient pressure spikes upon gas switching, due to the charged gaslines, would only help the initial stages of chemisorption or surfacereaction.

Practitioners will appreciate that alternative embodiments of valvesystems for gas delivery to reactor 100 are possible. In the embodimentshown in FIG. 18, two separate gas sources are shown providing thecarrier gas and the purge gas, which may be different gases. It ispossible, however, that in some embodiments the same gas used as thepurge gas may be used as the carrier gas for the precursor. In thiscase, separate gas sources may be used as shown in FIG. 18, or first gassource 226 may be used singly in a valve system 254, which has manysimilar components to valve system 224 of FIG. 18, as shownschematically in FIG. 19. Valve system 254 can be simplified byreplacing three-way valve 230 with a T-junction 256 as shownschematically in FIG. 20 for a valve system 258, which has many similarcomponents to valve system 224 of FIG. 18. As in valve system 224 ofFIG. 18, showerhead three-way valves 148 in valve system 254 (FIG. 19)and valve system 258 (FIG. 20) control the flow of purge gas orcarrier-plus-precursor gas to chamber 12. As shown in valve system 254(FIG. 19) and valve system 258 (FIG. 20), pump 236 may not be used insome embodiments.

In some embodiments, gas delivery of multiple precursors may bedesirable. Two embodiments of multiple precursor delivery are shown inthe schematic diagrams of a valve system 260 in FIG. 21 and a valvesystem 262 in FIG. 22. Valve systems 260 (FIG. 21) and 262 (FIG. 22)each have many similar components to valve system 224 of FIG. 18. Valvesystems 260 (FIG. 21) and 262 (FIG. 22) are shown configured for twoprecursor sources, but may be further adapted for additional precursorsources. In each of valve systems 260 (FIG. 21) and 262 (FIG. 22), asecond three-way valve 264 controls the flow of carrier gas to a secondprecursor source 266. A fourth on/off valve 268, a fifth on/off valve270, and a sixth on/off valve 272 are coupled similarly to, and operatesimilarly to, valves 240, 242, and 244, respectively, to control theflow of carrier gas through second precursor source 266. A gas line 274,similar to gas line 248, is coupled between three-way valve 264 andon/off valve 270.

In FIG. 21, valve system 260 further includes a third gas source 276 inaddition to first and second gas sources 226 and 228 of valve system 224of FIG. 18. A third three-way valve 278, coupled to on/off valve 272 viaa gas line 280, controls delivery of the second precursor to showerheadthree-way valve 148 via a gas line 282. A fourth three-way valve 284controls delivery of the purge gas via gas line 252 and a gas line 286to three-way valve 278, which directs the purge gas to showerheadthree-way valve 148 as needed via gas line 282.

In FIG. 22, valve system 262 is shown configured to use gas source 226for both the purge and carrier gases. The carrier gas is delivered fromgas source 226 to three-way valve 264 via a gas line 288. The purge gasis delivered to the second terminal of a third three-way valve 278 (andsimilar valves of any additional precursor sources) via gas line 252.The third terminal of three-way valve 278 is coupled to the secondterminal of showerhead three-way valve 148 via gas line 282. Three-wayvalve 278 thus controls delivery of the second precursor and the purgegas to showerhead three-way valve 148.

Other modifications may be made for alternative embodiments of the valvesystems of FIGS. 18, 19, 20, 21, and 22. The functions of showerheadthree-way valve 148 may be accomplished instead with an equivalentnetwork of on/off valves (similar to valves 240, 242, and 244) andfittings. Metering valves may be added to branches to regulate the flowfor specific branches. Pressure sensors may be added to branches andcoupled with the valve actuation to introduce known amounts of reactant.Valve timing may be manipulated to deliver “charged” volumes of gas toprocess chamber 12. The traditional valves may be replaced with advanceddesigns such as micro-electromechanical (MEM) based valves or valvenetworks. The entire valve system can be heated to prevent condensationof reactants in the network.

FIG. 23 is a perspective cross-section of two embodiments of ashowerhead 172 for gas distribution. Showerhead 172 is designed to havea larger diameter, and thus a larger area, than substrate 8 and ESC 6(FIG. 13). Showerhead 172 includes a plurality of mounting holes 290used to facilitate attachment of showerhead 172 to chamber lid 10 with aplurality of fasteners (see FIG. 13). Showerhead 172 also includes aplurality of pressure sensor orifices 166, one for each pressure sensorused to sense the pressure in process chamber 12. For example, fastchamber pressure sensor 142 and precision chamber pressure sensor 144(FIG. 8) would each require a pressure sensor orifice 166 in showerhead172. Showerhead 172 also includes showerhead lip 174 peripherally aroundthe edge of showerhead 172 used to prevent shadow ring 28 from hittingshowerhead 172.

Showerhead 172 also includes a cavity 292 centrally located in an uppersurface of showerhead 172 as shown in FIG. 23( a). Cavity 292 formsplenum 170 (FIG. 13) upon attachment of showerhead 172 to chamber lid10. A plurality of showerhead gas orifices 176 are arranged withincavity 292 in a pattern designed for a particular gas flow distribution.The diameter of cavity 292 is designed to be larger than the diameter ofsubstrate 8 (FIG. 13). In the embodiment of FIG. 23( b), showerhead 172includes a cavity 294 that is similar to cavity 292 of FIG. 23( a), butcavity 294 has a diameter designed to be smaller than the diameter ofsubstrate 8. Practitioners will appreciate that a number of differentdiffusing devices may be used to tailor the directionality of the gasflows as needed.

As mentioned above, gas may also be introduced into process chamber 12through shield 14. This allows cylindrical gas introduction around thevolume of process chamber 12 as discussed above with reference to FIG.4. FIG. 24 is a perspective cross-section of an embodiment of a shieldassembly 296, including a shield gas channel 40, for ALD reactor 100 ofFIG. 8. A plurality of shield support legs 16 attach to shield cap 196,which is attached to the base of shield 14. Most of shield support legs16 are solid. Gas is introduced into shield 14, through at least onehollow shield support leg 298, which extends through shield cap 196 intoshield gas channel 40 in shield 14.

Shield gas channel 40 is annular and runs completely around the base ofshield 14. Shield gas channel 40 is a high conductance channel thatallows introduced gas to distribute evenly around shield gas channel 40of shield 14 before introduction into process chamber 12 (FIG. 13). Gasis introduced to chamber 12 through a plurality of gas flow orifices300, which are evenly spaced along shield gas channel 40 and extendthrough an inner wall of shield 14 into process chamber 12. The gasintroduction path of shield assembly 296 is designed to ensure uniformgas flow around substrate 8 as discussed with reference to FIG. 4.

Introduction of gas through shield 14 allows tremendous flexibility indesigning ALD processes. In some embodiments, the same gas introducedthrough showerhead 172 can be simultaneously introduced through shield14 to provide improved coverage in process chamber 12 and on substrate 8(FIG. 13). Alternatively, in some embodiments, one gas can be introducedthrough showerhead 172 while a different gas is introduced throughshield 14, allowing improved gas isolation and quicker cycling of thegases.

Movement of shield 14, either before or during the gas flow, allows gasto be introduced at different planes within process chamber 12, parallelto the plane of substrate 8. The shield motion can be used to optimizethe gas flow distribution of a particular ALD process.

As discussed previously, another role of shield 14 is to confine plasma194 during processing (FIG. 13), which can result in heating of shield14. To maintain the shield at an acceptable process temperature, acooling/heating channel can be incorporated in the shield design. Thisalso helps prevent deposition on shield 14.

FIG. 25 is a perspective cross-section of an embodiment of a shieldassembly 302, including a shield cooling/heating channel 304, for ALDreactor 100 of FIG. 8. Shield assembly 302 includes some shield supportlegs 16, which are solid, attached to shield cap 196 at the base ofshield 14. Similar to shield assembly 296 of FIG. 24, which includes gaschannel 40, a cooling or heating fluid flows up into shield 14 throughat least one hollow shield support leg 306, which extends through shieldcap 196 into cooling/heating channel 304 in shield 14. Shieldcooling/heating channel 304 is annular and runs about two-thirds of theway around the base of shield 14. The cooling or heating fluid flowsdown, out of shield 14, through at least one other hollow shield supportleg (not shown), which is similar to hollow shield support leg 306.

Cooling or heating of shield 14 using a fluid flowing in cooling/heatingchannel 304 also allows improved control of the temperature of gasesintroduced into process chamber 12 through shield 14. FIG. 26 is aperspective cross-section of an embodiment of a shield assembly 308,including both shield gas channel 40 and shield cooling/heating channel304, for ALD reactor 100 of FIG. 8. In the embodiment shown in FIG. 26,gas channel 40 is located above cooling/heating channel 304. Hollowshield support leg 306 extends through shield cap 196 intocooling/heating channel 304 to allow fluid flow. Hollow shield supportleg 298 extends through shield cap 196 and cooling/heating channel 304into gas channel 40 to allow gas introduction from shield 14 intoprocess chamber 12 via gas flow orifices 300.

Practitioners will appreciate that shield assembly 308 could includealternative arrangements of gas channel 40 and cooling/heating channel304, including multiple gas channels 40 and/or multiple cooling/heatingchannels 304.

Design of particular shield assembly embodiments is extremely flexible,and reactor 100 is designed to facilitate removal, replacement, and useof various shield assemblies. This allows the easy introduction of ashield assembly that might include gas delivery and cooling/heating(i.e., shield assembly 308), or only one of these (i.e., shieldassemblies 296 or 302), or neither gas delivery nor cooling/heating,depending on the requirements of the customer and the process.

Electrostatic Chuck Assembly Design

ALD processes in the disclosed embodiments are ion-induced (see, forexample, application Ser. No. 09/812,352, application Ser. No.09/812,486, and application Ser. No. 09/812,285, referenced above),rather than thermally induced, through use of plasma 194 generated inprocess chamber 12 (FIG. 11 and FIG. 13). This allows deposition atlower temperatures than in conventional ALD systems, allowingreplacement of conventional heated susceptors with an electrostaticchuck (ESC) assembly 106 to retain substrate 8. ESC assembly 106 may befurther designed for improved temperature control and improved radiofrequency (RF) power coupling.

FIG. 27A is a cutaway perspective view of an embodiment of anelectrostatic chuck assembly 106 for ALD reactor 100 of FIG. 8. ESCassembly 106 includes in part, an electrostatic chuck (ESC) 6, a coolingplate 110, and a baseplate 112. Cooling plate 110 and baseplate 112 canbe shaped as annuli with overlapping central orifices that togetherdefine an access port 310, which provides access to a central region ofthe underside of ESC 6.

Substrate 8 rests on an annular sealing lip 46, peripherally surroundinga top surface 50 of ESC 6. Annular sealing lip 46 holds substrate 8above surface 50 defining a backside gas volume 48 bounded by surface50, sealing lip 46, and the backside of substrate 8.

A backside gas is provided to gas volume 48 through a backside gas entry312 to a backside gas valve 154. Gas valve 154 is located on theexterior underside of reactor 100 at the outer edge of baseplate 112 toprovide easy access (FIG. 8 and FIG. 11). The backside gas flows along abackside gas line 54, which runs radially inward along a lower surfaceof baseplate 112. Gas line 54 curves upward through access port 310 andis attached to the center of the bottom surface of ESC 6 using abackside gas line flange 314. The backside gas flows through a backsidegas passageway 56 centrally located in and extending through ESC 6 togas volume 48. A backside gas line seal 316 inside flange 314 maintainsthe pressure of gas volume 48. The backside gas plays an important rolein the temperature control of substrate 8.

Electrostatic chucks are usually made of a dielectric material (e.g.,aluminum nitride AlN, or polyimide). ESC 6 may be designed to have itsbulk material effects dominated by the Johnson-Rahbek (JR) effect ratherthan a coulombic effect, since the JR effect provides a stronger, moreefficient electrostatic attraction. A JR ESC typically has a bulkresistivity between 10⁸ and 10¹² Ω-cm, while a coulombic ESC generallyhas a bulk resistivity greater than 10¹³ Ω-cm.

Embedded in the dielectric material of ESC 6, close to top surface 50,are at least two electrodes. A first electrode 80 and a second electrode82 are shaped as concentric annular plates made of a conductivematerial, for example, tungsten or molybdenum. First electrode 80 isbiased using a first electrode terminal 318, which is coupled to firstelectrode 80 and extends down through ESC 6 into access port 310. Secondelectrode 82 is biased using a separate second electrode terminal (notshown). A DC “chucking” voltage is applied to both first electrode 80and second electrode 82 to create an electrostatic attraction betweensubstrate 8 and top surface 50 of ESC 6 to retain substrate 8 duringprocessing. Simultaneously, RF bias power is coupled to each electrode80 and 82 as well. The RF bias power provides the power for plasma andhence ion generation during modulated ion induced atomic layerdeposition.

In addition to generating a plasma, the RF bias power also induces aslight negative potential (e.g., a DC offset voltage typically −10 V to−80 V at ≦150 W RF power and 0.1-1 Torr pressure) on substrate 8. Themagnitude of the potential should be ≦150 V. The induced voltage definesthe ion energy of the positively charged ions in the plasma and attractsthe positively charged ions toward the surface of substrate 8. Thepositively charged ions impinge on the wafer, driving the depositionreaction and improving the density of the deposited film.

A resistive heater 72 is also embedded in ESC 6. Resistive heater 72 isshaped as at least one coil or ribbon that winds throughout ESC 6 in aplane located about midway between electrodes 80 and 82 and the bottomof ESC 6. Heater 72 is controlled via at least one resistive heaterterminal 320 coupled to heater 72. Terminal 320 extends down through ESC6 into access port 310. Thus, ESC 6 is basically a dielectric substratesupport with an embedded heater 72 and embedded electrodes 80 and 82 forDC biasing and RF power coupling.

ESC 6 is held in contact with cooling plate 110 using an annular clampring 178, which overlaps a clamp land 322 of a surrounding flange at thebase of ESC 6. An ESC O-ring 324 creates a vacuum seal between ESC 6 andcooling plate 110. A plurality of clamp ring fasteners 180, eachextending through clamp ring 178 into cooling plate 110, secure theconnection between ESC 6 and cooling plate 110. A process kit 182,having an annular elbow shape, fully surrounds clamp ring 178 covering atop surface and a side surface of clamp ring 178. Process kit 182includes a process kit bevel 202 used for centering a shadow ring 28(FIG. 15) on process kit 182. Process kit 182 may be made of adielectric material (e.g., aluminum oxide, aluminum nitride, orhard-anodized aluminum) to electrically isolate clamp ring fasteners 180from ESC 6 and substrate 8. Process kit 182 also protects clamp ring 178and fasteners 180 from process gases, facilitating cleaning of reactor100 (FIG. 12).

Cooling plate 110 can be made (e.g., machined) from a variety ofthermally conductive materials, for example, aluminum or stainlesssteel. An upper surface of cooling plate 110 is patterned to create aplurality of small area contacts 326 and a plurality of thermal breaks184. Contacts 326, which have the form of ridges, contact the bottomsurface of ESC 6. Thermal breaks 184 are gaps between ESC 6 and coolingplate 110, which increase the temperature difference between ESC 6 andcooling plate 110. The temperature of cooling plate 110 can becontrolled using a fluid (e.g. water) flowing in a plurality of coolantchannels 78. Coolant channels 78 are designed to allow the fluid to flowin a largely circular manner at various diameters of cooling plate 110.

A lower surface of cooling plate 110 is attached to an upper surface ofbaseplate 112. The upper surface of baseplate 112 forms the lower wallsof coolant channels 78 in cooling plate 110. Baseplate 112, which may bemade of aluminum, provides structural support for ESC assembly 106.Thermal breaks 184 of cooling plate 110 allow maintenance of asignificant temperature difference between top surface 50 (which may benear 300° C.) of ESC 6 and a bottom surface of baseplate 112 (which isexposed to air and may be less than 50° C.).

One of a plurality of lift pins 108, which facilitate loading andunloading of substrate 8, is shown in retracted process position, withthe tip of lift pin 108 below top surface 50 of ESC 6. Each lift pin 108extends through a lift pin orifice 328, which includes a plurality ofaligned orifices in baseplate 112, cooling plate 110, and ESC 6.

Alternative embodiments of ESC assembly 106 are possible. For example,in some embodiments, at least one peripheral ring of holes can be usedto introduce the backside gas, rather than just a centrally locatedhole, as discussed in more detail below. In addition, in someembodiments, ESC 6 can be replaced with a conventional susceptor tofacilitate ALD processes at higher temperatures.

FIG. 27B illustrates interdigitated electrodes 79 and 83, and FIG. 27Cillustrates D-shaped electrodes 85 and 87, that may be used instead ofthe concentric annular plate electrodes 80 and 82 in FIG. 27A.Electrodes 85 and 87 may be solid or have an opening, such as shown bydashed lines. Practitioners will appreciate that various otherembodiments of the electrodes are possible.

In one embodiment, the showerhead 172 (FIG. 23) is not grounded but iscoupled to another RF source in a manner similar to the RF sourcecoupling to the ESC electrodes in FIG. 7. The phase difference betweenthe RF power applied to showerhead 172 and the RF power coupled toelectrodes 80 and 82 in the ESC controls ion density and energy, with adifference of 180° creating the maximum ion density and energy. Inanother embodiment, the two RF sources have different frequencies.

Temperature Control of Electrostatic Chuck Assembly

Temperature control of ESC assembly 106 (FIG. 27A) is important for highquality atomic layer deposition. A uniform temperature across asubstrate 8 resting on annular sealing lip 46 of ESC 6 promotes uniformchemisorption of precursors. If the temperature of substrate 8 is toohigh, decomposition or desorption of precursors may occur. If thetemperature of substrate 8 is too low, either or both of thechemisorption and the deposition reactions will be impeded.

FIG. 28 is a schematic diagram of a control system 330 for electrostaticchuck (ESC) assembly 106 (FIG. 27A) of ALD reactor 100 of FIG. 8.Control system 330 may also be applied to various embodiments ofpedestal 4 of ALD reactor 2 of FIG. 1. Control system 330 is anembodiment of control system 44 of FIG. 6, as discussed previously.

Control system 330 is used to establish and maintain a uniformtemperature across substrate 8. As shown in FIG. 28, substrate 8 restson an annular sealing lip 46 defining a backside gas volume 48 betweensubstrate 8 and top surface 50 of ESC 6. A backside gas (e.g., Ar, He,etc.) is usually chosen from among the species in chamber 12 to preventcontamination in the deposited film. The backside gas flows from abackside gas source 52 along a backside gas line 54, through a backsidegas passageway 56 in ESC 6, and into gas volume 48.

The backside gas improves the thermal contact between substrate 8 andESC 6, by providing a medium for thermal energy transfer betweensubstrate 8 and ESC 6. Heat transfer improves with increasing backsidegas pressure, up to a saturation limit. Ranges for backside gaspressures are 3-20 torr, and typical ranges are 6-10 torr for goodthermal conductivity and temperature uniformity across the substrate.Using the disclosed embodiments, a temperature uniformity across thesubstrate may be ≦5° C. Above a backside gas pressure of 5 torr, auniformity of ≦15° C. is typically achieved. A pressure controller 58maintains the backside gas at a constant pressure, thus ensuringconstant heat transfer and uniform substrate temperature. In practice,annular sealing lip 46 may take the form of several islands scatteredacross top surface 50 of ESC 6. This introduces a leak rate of thebackside gas that must be taken into account. The amount of directcontact between the chuck and the substrate can be virtually any amount,such as between 15-50%.

The temperature of substrate 8 is modulated by heating or cooling ESC 6.A temperature sensor 60 (e.g., a thermocouple or optical infraredsensor) is coupled via a sensor connection 62 to a temperature monitor64 in a closed loop feedback control circuit 332. A temperature setpointsignal is also provided to monitor 64 via a setpoint electricalconnection 334. A temperature controller 66 creates a signal that isamplified through a power amplifier or modulator 336 and applied via anelectrical connection 70 to a resistive heater terminal 320 (FIG. 27A),which is coupled to a resistive heater 72 embedded in ESC 6. A coolanttemperature and flow controller 74, as is widely known, controls thefluid from a coolant supply 76 as it flows in a plurality of coolantchannels 78 in pedestal 4 (or in ESC assembly 106 in FIG. 12 and FIG.13).

Control system 330 is designed to control the temperature of substrate8, by heating and/or cooling, for a wide range of power and temperature.Temperature control can be accomplished by various techniques, includingregulating the backside gas pressure, heating ESC 6 directly withresistive heater 72, or regulating the temperature and/or flow of fluidin coolant channels 78. The temperature of substrate 8 can thus beperiodically or continuously varied during the deposition process tomeet different process demands. Additional information regardingtemperature control in atomic layer deposition may be found in relatedU.S. application Ser. No. 09/854,092, entitled “Method And Apparatus ForImproved Temperature Control In Atomic Layer Deposition,” filed May 10,2001.

Alternative embodiments of control system 330 of FIG. 28 are possible.For example, the temperature control system of circuit 332 may havevarious embodiments. In addition, temperature sensor 60 may have variousembodiments. Temperature sensor 60 may be a thermocouple that measuresthe temperature of ESC 6. Temperature sensor 60 may be a pyrometerdevice that optically measures the temperature of the backside ofsubstrate 8. Or, temperature sensor 60 could take other equivalentforms.

In some embodiments of control system 330 of FIG. 28, an alternativeenergy source may be included as another option to control thetemperature of substrate 8. FIG. 29 is a schematic diagram of a controlsystem 338, including an alternative energy source 340, for pedestal 4of reactor 2 (FIG. 1) or for ESC assembly 106 (FIG. 27A) of ALD reactor100 (FIG. 8). Control system 338 is similar to control system 44 (FIG.6) and control system 330 (FIG. 28), as discussed previously.Alternative energy source 340 is located outside of pedestal 4 (or ESCassembly 106) near the top of chamber 12 and may include radiation fromlamps, a plasma, or another source. Alternative energy source 340 couldbe controlled, for example, by regulating the power to the lamps orplasma. Alternative energy source 340 could be used alone, or inconjunction with one or more of resistive heater 72, the fluid incoolant channels 78, or the pressure of the backside gas in gas volume48.

In some embodiments, an additional cooling source may be added tocontrol system 330 of FIG. 28 to improve the cooling capacity and/orperformance. The additional cooling source could be a refrigerationsystem, a heat pipe, a refrigerated liquid or gas coolant system, orother equivalent system.

In some embodiments of control system 330 of FIG. 28, the backside gasmay be introduced to gas volume 48 through multiple orifices rather thanjust a centrally located orifice. FIG. 30 is a perspective view of anembodiment of a portion 342 of an ESC assembly 106 (FIG. 27A) for ALDreactor 100 of FIG. 8. ESC 6 includes a central orifice 344 as well as aperipheral ring of orifices 346 located near the periphery of substrate8. Various embodiments of ESC 6 may include either or both of orifice344 and orifices 346. Orifices 346 result in improved pressureuniformity between substrate 8 and ESC 6, which results in improvedtemperature uniformity across substrate 8. An additional peripheral ringof orifices 347 can be added outside of orifices 346 to ensure aconstant pressure gradient at the edge of substrate 8. The additionalring of orifices would also serve as an edge purge to prevent reactivegases from entering gas volume 48 (FIG. 28) and causing deposition onthe backside of substrate 8.

In some embodiments of control system 330 of FIG. 28, pressurecontroller 58 may be replaced by, for example, a flow regulator such asa metering valve or mass flow controller. In still other embodiments, anactuation valve can be added between pressure controller 58 and backsidegas volume 48 to isolate pressure controller 58 and gas source 52 fromprocess chamber 12 during a substrate transfer. This valve mayadditionally be used to stop the flow of backside gas to reduce itspressure, allowing the substrate to “de-chuck” without “popping”(shifting) when electrodes 80 and 82 in ESC 6 are de-powered. This valvemay additionally be used in conjunction with a pump to more quicklyreduce the backside gas pressure before “de-chucking” substrate 8.

Practitioners will appreciate that various other embodiments of controlsystem 330 and its various constituents are possible.

Electrical Biasing and Plasma Generation Using Electrostatic ChuckAssembly

FIG. 31 is a schematic diagram of a circuit 348 for electrical biasingof electrostatic chuck (ESC) 6 of ESC assembly 106 (FIG. 27A) of ALDreactor 100 of FIG. 8. Circuit 348 may also be applied to variousembodiments of ESC 6 of pedestal 4 of ALD reactor 2 of FIG. 1. Circuit348 is an alternative embodiment to circuit 84 of FIG. 7, as discussedpreviously.

As shown in FIG. 31, ESC 6 includes at least a first electrode 80 and asecond electrode 82. One possible embodiment of the electrode geometryof first and second electrodes 80 and 82 (shown schematically in FIG.31) is shown in FIG. 27A, where first and second electrodes 80 and 82are shown as concentric annular plates. A double D (i.e., mirror imaged)configuration or interdigitated configuration for electrodes 80 and 82can also be used, as previously mentioned. In FIG. 31, first and secondelectrodes 80 and 82 are each biased with a DC voltage. RF bias power isalso coupled to both electrodes 80 and 82. Embedding electrodes 80 and82 in ESC 6 allows improved RF power coupling to substrate 8 withmaximum uniformity and minimal power loss, compared to applying RF powerto cooling plate 110 (or baseplate 112) upon which ESC 6 sits (FIG.27A). This is because electrodes 80 and 82 in ESC 6 are close tosubstrate 8, while cooling plate 110 (and baseplate 112) arecomparatively far from substrate 8.

First electrode 80 and second electrode 82 are biased with different DCpotentials to provide the “chucking” action that holds substrate 8 toESC 6 prior to plasma ignition and during deposition. As shown in FIG.31, first electrode 80 is coupled via a serial coupling of a firstinductor 88 and a first load resistor 350 to one terminal of a DC powersupply 86. Second electrode 82 is coupled via a serial coupling of asecond inductor 90 and a second load resistor 352 to the other terminalof DC power supply 86.

A third capacitor 354 is coupled between one terminal of inductor 88 anda ground terminal 94. A fourth capacitor 356 is coupled between theother terminal of inductor 88 and ground terminal 94. A fifth capacitor358 is coupled between one terminal of inductor 90 and ground terminal94. A sixth capacitor 360 is coupled between the other terminal ofinductor 90 and ground terminal 94. Inductor 88 and capacitors 354 and356 together form an RF trap circuit 362, which filters RF from the DCbias. Similarly, inductor 90 and capacitors 358 and 360 together formanother RF trap circuit 362.

RF power is also supplied to both first electrode 80 and secondelectrode 82 using an RF generator 92 with one terminal coupled toground terminal 94. A third inductor 364 is coupled between the otherterminal of RF generator 92 and one terminal of a first variablecapacitor 366. The other terminal of variable capacitor 366 is coupledto one terminal of a first capacitor 96 and to one terminal of a secondcapacitor 98. The other terminal of capacitor 96 is coupled to firstelectrode 80. The other terminal of capacitor 98 is coupled to secondelectrode 82. A second variable capacitor 368 is coupled across theterminals of RF generator 92, between one terminal of inductor 364 andground terminal 94. Inductor 364 and capacitors 366 and 368 togetherform an RF impedance matching circuit 370, which minimizes the reflectedpower to RF generator 92.

Circuit 348 of FIG. 31 allows simultaneous application of a DC“chucking” voltage and of an RF power for plasma generation duringprocessing. The same RF power is used to create plasma 194 abovesubstrate 8 (FIG. 13) and to generate a negative, induced DC bias onsubstrate 8. RF power can be used since the breakdown voltage requiredto generate plasma 194 using RF power is far lower than in the DC case(e.g., 100 V vs. 300-400 V) for a given Paschen curve ofpressure-distance product (P x d). In addition, a stable DC bias can beinduced using RF power. Of course, it is possible to generate plasma 194using a high DC voltage instead of RF power, with appropriatemodifications to the biasing hardware (see, for example, the discussionof FIG. 40 below).

In FIG. 31, coupling RF power to electrodes 80 and 82 allows a uniformpotential to build across substrate 8 while employing low RF powers, forexample, 50 W to 150 W, which is less than the 350 W to 600 W requiredin conventional plasma reactors. The frequency of the RF bias power canbe 400 kHz, 13.56 MHz, or higher (e.g., 60 MHz, 200 MHz). The lowfrequency, however, can lead to a broad ion energy distribution withhigh energy tails which may cause excessive sputtering. The higherfrequencies (e.g., 13.56 MHz or greater) lead to tighter ion energydistributions with lower mean ion energies, which is favorable formodulated ion-induced ALD deposition processes. The more uniform ionenergy distribution occurs because the bias polarity switches beforeions can impinge on substrate 8, such that the ions see a time-averagedpotential.

In conventional plasma reactors, RF power is applied to the top boundaryof the process chamber, usually a showerhead. This causes sputtering ofthe top boundary, which is a major source of impurity incorporation(typically aluminum or nickel) and/or particulate incorporation inconventionally deposited films. The sputtering also transfers kineticenergy to the reactor structure, heating it considerably and requiringactive cooling of the reactor structure.

In the present embodiments, RF power is applied to electrodes 80 and 82(FIG. 31) embedded in ESC 6 of ESC assembly 106 of ALD reactor 100 (FIG.12), rather than to showerhead 172 (FIG. 13). This minimizes sputteringof showerhead 172 and allows better control of the bias induced onsubstrate 8. It also avoids excessive heating of chamber lid 10,minimizing any cooling requirements.

Referring to FIG. 13, showerhead 172 and shield 14 are grounded so thatthe higher plasma sheath voltage drop is localized mostly on substrate 8where deposition takes place. This is because the voltage ratioV_(hot)/V_(cold) is proportional to the respective electrode areasaccording to (A_(cold)/A_(hot))^(n), where n is greater than one.V_(hot) is the plasma sheath voltage drop at the powered, or “hot,”electrode, that is, ESC 6 of ESC assembly 106. V_(cold) is the voltagedrop at the non-powered, or “cold,” electrode, that is, showerhead 172and shield 14. The combined areas of showerhead 172 and shield 14 can bejointly considered as the area of the cold electrode. This is becausethe small volume of process chamber 12 results in a showerhead 172 toESC 6 spacing that is small (nominally 0.3 to 0.6 inches) so that thepowered electrode can “see” showerhead 172 and shield 14 as a singleground reference. Taken together, these combined areas are larger thanthe area of substrate 8, or the area of the hot electrode. Thus, forthis reactor, A_(cold)/A_(hot)>1.

In addition, by applying RF power to ESC 6 via electrodes 80 and 82(FIG. 31), a low RF power can be used to simultaneously generate plasma194 (FIG. 13) and to keep the energy of the impinging ions from plasma194 low and controlled. The ion energy is given byE=e|V_(p)|+e|V_(bias)|, where V_(p) is the plasma potential and V_(bias)is the bias voltage induced on substrate 8. The ion energy should be≦150 eV, and preferably between 10-80 eV, to drive the depositionreaction. The magnitude of V_(bias) should be<150V, and preferablyV_(bias) should be between −10 and −80V, to prevent sputtering of thedeposited layer. The magnitude of V_(p) is typically 10-30V.

The induced bias voltage is controlled by the applied RF power. Theinduced bias voltage increases with increasing RF power and decreaseswith decreasing RF power. Increasing the RF power also generallyincreases the number of ions generated.

Controlling the RF power also controls the density of ions in theplasma. Higher RF powers are required for larger substrate diameters.The preferred power density is ≦0.5 W/cm², which equates toapproximately ≦150 W for a 200 mm substrate. Power densities ≧3 W/cm²(greater than about 1000 W for a 200 mm diameter substrate) may lead toundesired sputtering of the deposited film.

Referring to FIG. 13, cooling plate 110 and baseplate 112 are grounded.Therefore, each clamp ring fastener 180 is also grounded. Process kit182, which is made of an insulating material, electrically shieldsfasteners 180 so that plasma 194 is not affected by the ground voltageof fasteners 180.

Plasma 194 can be controlled in a variety of ways. For example, plasma194 can be controlled by varying the applied RF power. In somealternative embodiments of circuits for electrical biasing of ESC 6 ofALD reactor 100 (FIG. 12 and FIG. 13), a switch may be included, forexample, in RF impedance matching circuit 370 or with RF generator 92(FIG. 31). FIG. 32 is a schematic diagram of a circuit 372, including anRF match switch 374 in RF impedance matching circuit 370, for electricalbiasing of ESC 6. FIG. 33 is a schematic diagram of a circuit 376,including an RF supply switch 378 in an RF power supply 380 (which alsoincludes RF generator 92), for electrical biasing of ESC 6. Circuit 372(FIG. 32) and circuit 376 (FIG. 33) are similar to circuit 348 (FIG.31), except for switches 374 and 378. Switches 374 and 378 can be openedto isolate RF generator 92, or switches 374 and 378 can be closed toapply RF power to electrodes 80 and 82. Switches 374 and 378 enable aplasma response time in the 100 ms time range.

Plasma 194 (FIG. 13) can also be controlled by varying gas pressurewhile using, for example, circuit 348 of FIG. 31 with an RF powerconstantly applied to electrodes 80 and 82. Referring to FIG. 15, FIG.16, and FIG. 17, as discussed previously, shield 14 forms a shieldconductance upper path 22 with showerhead 172 and chamber lid 10. Shield14 also forms a shield conductance lower path 24 with shadow ring 28.The conductances of upper and lower paths 22 and 24 are varied byprecision movement of shield 14 by linear motor 122 (FIG. 8).

The conductances of upper and lower paths 22 and 24 directly affect thepressure in process chamber 12 and can be used to vary that pressure.For example, a high pressure (i.e., relative to the pressure of annularpumping channel 20) can be established in chamber 12 using a lowconductance process shield position 210 as shown in FIG. 15. Highpressure will strike plasma 194 (FIG. 13) given a favorable ambient inchamber 12. A low pressure can be established in chamber 12 using apurge shield position 214, as shown in FIG. 17, to expose chamber 12 toannular pumping channel 20. Low pressure will effectively terminateplasma 194 since not enough gas phase collisions will occur to sustainplasma 194. Applying RF power to electrodes 80 and 82 at pressures thatwill not strike or sustain plasma 194 will cause 100% reflection of theoutput power from RF generator 92 (FIG. 31). Thus, RF generator 92should be capable of absorbing this power without detrimental effects.

Plasma 194 (FIG. 13) can also be controlled by a combination of varyinggas pressure and applied RF power. For example, plasma 194 may beignited by a high pressure and favorable ambient in chamber 12. Plasma194 may be terminated by a switch, such as switch 374 in circuit 372 ofFIG. 32 or switch 378 in circuit 376 of FIG. 33.

Practitioners will appreciate that various other embodiments of circuit348 of FIG. 31 and its various constituents, for electrical biasing ofESC 6, are possible. For example, multiple RF sources may be utilized.

ALD Processes: Background and Novel Processes

FIG. 34 is a schematic illustration of a conventional ALD process. In atypical ALD cycle, which usually includes four steps, each precursor (orreactant) is introduced sequentially into the chamber, so that no gasphase intermixing occurs. First, a first gaseous precursor 382 (labeledAx) is introduced into the deposition chamber, and a monolayer of thereactant is chemisorbed (or physisorbed) onto the surface of a substrate8 forming a chemisorbed precursor A 384 as shown in FIG. 34( a). A freeligand x 386 is created by the chemisorption of precursor Ax 382.Second, excess gaseous precursor Ax 382 and ligands x 386 are pumpedout, possibly with the aid of an inert purge gas, leaving the monolayerof chemisorbed precursor A 384 on substrate 8 as shown in FIG. 34( b).

Third, a second gaseous precursor 388 (labeled By) is introduced intothe deposition chamber. Precursor By 388 reacts with chemisorbedprecursor A 384 on substrate 8 as shown in FIG. 34( c) in aself-limiting surface reaction. The self-limiting reaction halts onceinitially adsorbed precursor A 384 fully reacts with precursor By 388.Fourth, excess gaseous precursor By 388 and any reaction by-products arepumped out, again possibly with the aid of an inert purge gas, leavingbehind an AB monolayer 390 of the desired thin film as shown in FIG. 34(d). A desired film thickness is obtained by repeating the depositioncycle as necessary. The film thickness can be controlled to atomic layer(i.e., angstrom scale) accuracy by simply counting the number ofdeposition cycles.

ALD processes, however, are slower than traditional depositiontechniques such as CVD and PVD. In order to improve throughput, shorterdeposition cycles are desirable. One way to shorten the deposition cycleis to shorten the durations of the individual precursor and pump/purgesteps. The individual pulse lengths, however, cannot be arbitrarilydecreased. The first precursor pulse must be long enough to form anadsorbed layer of the first precursor on the substrate. The secondprecursor pulse must be long enough to allow complete reaction betweenthe first and second precursors. The pump/purge pulses in between theprecursor pulses must be long enough so that gas phase intermixing ofthe precursors does not occur. Gas phase intermixing can lead to gasphase reactions and/or particle formation, each of which can causequality and reliability problems in the deposited film.

FIG. 35 is a schematic illustration of a novel ALD process. Onedeposition cycle includes two steps, rather than four, which improvesprocess throughput and repeatability. In the base process, a substrate 8is maintained at a precise temperature that promotes chemisorptionrather than decomposition.

In the first step, a gaseous precursor 392 is introduced into theprocess chamber. Gaseous precursor 392 includes the desired thin filmspecies (P) bonded with a plurality of ligands (L). Species P may be asingle element (e.g., Ti, W, Ta, Cu) or a compound (e.g., TiN_(x),TaN_(x), or WN_(x)). In the novel ALD process, a molecule of gaseousprecursor 392 interacts with a surface bond 394 to form a chemisorbedprecursor 396 via a chemical bonding process that may create a pluralityof free ligands 398 as shown in FIG. 35( a). As a result of the firststep, a monolayer of chemisorbed precursor 396 is formed on substrate 8as shown in FIG. 35( b).

In the second step, an inert purge gas is introduced into the processchamber to purge excess gaseous precursor 392. The purge gas mayinclude, for example, argon (Ar), diatomic hydrogen (H₂), and otheroptional species such as helium (He). RF power is applied (e.g., using acomputer synchronized switch) during this second step to generate aplasma 194 in the process chamber, or the plasma is struck by anincreased gas pressure under constant RF power. As shown in FIG. 35( c),plasma 194 includes a plurality of energetic ions 400 (e.g., Ar⁺ ions)and a plurality of reactive atoms 402 (e.g., H atoms). Some of reactiveatoms 402 may actually be ions.

Ions 400 and atoms 402 impinge on the surface of substrate 8. Energeticions 400 transfer energy to substrate 8, allowing reactive atoms 402 toreact with chemisorbed precursor 396 and to strip away unwanted ligands(which form a plurality of volatile ligands 404) in a self-cleaningprocess. Reactive atoms 402, in conjunction with energetic ions 400, maythus be considered to act as a “second” precursor. When the plasma poweris terminated, a monolayer 406, usually about one atomic layer of thedesired species P, is left on substrate 8 as shown in FIG. 35( d). Thistwo-step deposition cycle can be repeated as needed until the desiredfilm thickness is achieved. The film thickness deposited per cycledepends on the deposited material. Typical film thicknesses range from10-150 Å.

Typical precursors for tantalum (Ta) compounds include PDEAT[pentakis(diethylamido)tantalum], PEMAT[pentakis(ethylmethylamido)tantalum], TaBr₅, TaCl₅, and TBTDET[t-butylimino tris(diethylamino)tantalum]. Typical precursors fortitanium (Ti) compounds include TiCl₄, TDMAT[tetrakis(dimethylamido)titanium], and TDEAT[tetrakis(diethylamino)titanium]. Typical precursors for copper (Cu)compounds include CuCI and Cupraselect®[(trimethylvinylsilyl)hexafluoroacetylacetonato copper I]. Typicalprecursors for tungsten (W) compounds include W(CO)₆ and WF₆. Incontrast to conventional ALD processes, organometallic precursors can beused in novel ALD processes.

The purge pulse includes gas, or gases, that are inert (e.g., argon,hydrogen, and/or helium) to prevent gas phase reactions with gaseousprecursor 392. Additionally, the purge pulse can include the same gas,or gases, needed to form energetic ions 400 (e.g., Ar⁺ ions) andreactive atoms 402 (e.g., H atoms). This minimizes the gas switchingnecessary for novel ALD processes. Acting together, reactive atoms 402react with chemisorbed precursor 396, while energetic ions 400 providethe energy needed to drive the surface reaction. Thus, novel ALDprocesses can occur at lower temperatures (e.g., T<300° C.) thanconventional ALD processes (e.g., T˜400-500° C.). This is especiallyimportant for substrates that already include low thermal stabilitymaterials, such as low-k dielectrics.

Since the activation energy for the surface reaction is provided byenergetic ions 400 created in plasma 194 above substrate 8, the reactionwill not generally occur without the energy provided by ion bombardmentbecause the process temperature is kept below the temperature requiredfor thermal activation. Thus, novel atomic layer deposition processesare ion-induced, rather than thermally induced. The deposition reactionis controlled by modulation of the energy of energetic ions 400, bymodulation of the fluxes of energetic ions 400 and reactive atoms 402impinging on substrate 8, or by modulation of both energy and fluxes.The energy (e.g., 10 eV to 100 eV) of energetic ions 400 should be highenough to drive the surface reaction, but low enough to preventsignificant sputtering of substrate 8.

Timing diagrams for (a) a typical prior art ALD process and (b) a novelALD process are compared in FIG. 36. FIG. 36( a) shows that onedeposition cycle in a conventional ALD process includes a firstprecursor pulse 408, a purge/pump pulse 410, a second precursor pulse412, and another purge/pump pulse 410. Each pulse is followed by a delay414, which has a duration that is usually non-zero. Delays 414, duringwhich only pumping occurs and no gases flow, are additional insuranceagainst gas phase intermixing of first precursor pulse 408 and secondprecursor pulse 412. Delays 414 also provide time to switch gases withconventional valve systems.

The durations of first and second precursor pulses 408 and 412 may bebetween 200 ms and 15 sec. The duration of purge/pump pulses 410 may be5-15 sec. The durations of delays 414 may be 200 ms to 5 sec. Thisresults in deposition cycles from 11 sec to 75 sec. Thus, a 50 cycledeposition process could take over one hour.

FIG. 36( b) shows two deposition cycles in the novel ALD process. Onedeposition cycle includes a first precursor pulse 416 and a purge gaspulse 418. Each pulse is followed by a delay 420. The elapsed time ofone deposition cycle is significantly shorter in accordance with thenovel process when compared to conventional ALD processes, therebyincreasing process throughput.

Process throughput can be further increased if delays 420 have zerolength. Zero-length delays can be accomplished using three-way valves(in particular showerhead three-way valve 148 of FIG. 8) or a similarconfiguration of on/off valves and fittings, which allow fast gasswitching. Delays 420 of zero length are further facilitated in novelALD processes by effective use of purge gas pulse 418, which may includea mixture of more than one gas. For example, the purge gas may includethe “second” precursor source gas(es) (i.e., as shown in FIG. 35( c),reactive atoms 402, acting in conjunction with energetic ions 400,created during purge gas pulse 418). Additionally, the carrier gas forthe first precursor (i.e., flowing during first precursor pulse 416) maybe one of the source gases of the “second” precursor.

Practitioners will appreciate that alternative embodiments of novel ALDprocesses are possible. For example, in some embodiments, multipleprecursors for compound thin films might be employed in otherembodiments, Ihe deposition cycle of FIG. 36( b) might begin with apurge gas pulse 418, including a plasma, used as an in-situ clean toremove carbon-containing residues, native oxides, or other impurities.In these embodiments, reactive atoms 402 (e.g., H atoms in FIG. 35( c))react with carbon and oxygen to form volatile species (e.g., CH_(x) andOH_(x) species). Energetic ions 400 (e.g., Ar⁺ and/or He⁺ ions in FIG.35( c)) improve dissociation (e.g., of H₂) and add a physical clean(e.g., via sputtering by Ar⁺ ions generated in the plasma). In stillother embodiments, reactive atoms 402 may not be needed and plasma 194may not include reactive atoms 402.

Additional information regarding in-situ cleaning in atomic layerdeposition may be found in related U.S. Provisional Application Ser. No.60/255,812, entitled “Method For Integrated In-Situ Cleaning AndSubsequent Atomic Layer Deposition Within A Single Processing Chamber,”filed Dec. 15, 2000.

Alternative Novel ALD Processes

The novel ALD process described previously may be modified to furtherincrease performance. Alternative novel ALD processes may address fasterpurging of precursors, rapid changes in the conductance of the processchamber, state-based changes from one step to the next,self-synchronization of the process steps, and/or various plasmageneration and termination options. Such alternatives can be used tofurther decrease the length of a deposition cycle, thereby increasingthroughput.

For example, in some novel ALD process embodiments, it is desirable toquickly purge a gaseous precursor 392 from the process chamber afterformation of a monolayer of chemisorbed precursor 396 on substrate 8(FIG. 35( b)). This can be accomplished using the in-process tunableconductance achieved by shield 14 (FIG. 13), which can be moved duringthe deposition cycle. Referring to FIG. 15, FIG. 16, and FIG. 17, asdiscussed previously, shield 14 forms shield conductance upper path 22with showerhead 172 and chamber lid 10. Shield 14 also forms shieldconductance lower path 24 with shadow ring 28. The conductances of upperand lower paths 22 and 24 are varied by precision movement of shield 14by linear motor 122 (FIG. 8).

It is possible, therefore, to rapidly increase the chamber conductanceby lowering shield 14 after exposing substrate 8 to gaseous precursor392. For example, a purge shield position 214 may be used (FIG. 17).Lowering shield 14 opens up shield conductance upper and lower paths 22and 24 to annular pumping channel 20. The low pressure of pumpingchannel 20 will hasten removal of excess gaseous precursor 392, andby-products such as free ligands 398 (FIG. 35( b)), from process chamber12. Simultaneously, the purge gas (e.g., Ar, H₂, and/or He) is flowed toassist in purging excess gaseous precursor 392 and by-products fromchamber 12. Lowering shield 14 also leads to a drop in the pressure inchamber 12 through exposure of chamber 12 to annular pumping channel 20.Shield 14 can then be moved back up, for example, to a position similarto shield position 212 of FIG. 16, to decrease the conductance and raisethe pressure in chamber 12 (assuming constant gas flow) in order tostrike plasma 194 (FIG. 35( c)).

In particular, plasma 194 can be generated while using, for example,circuit 348 of FIG. 31. Application of RF power may be synchronized(e.g., by computer control) with the position of shield 14 (FIGS. 15-17)to generate plasma 194 in chamber 12 (FIG. 13). Alternatively, if RFbias power is constantly applied to electrodes 80 and 82 using circuit348 (FIG. 31), high pressure (i.e., relative to the pressure of annularpumping channel 20) in process chamber 12 can be used to trigger plasma194 (FIG. 13). Low pressure (i.e., near the pressure of annular pumpingchannel 20) will effectively terminate plasma 194 since not enoughcollisions will occur to sustain plasma 194.

FIG. 37 shows timing diagrams for an alternative ALD process embodiment,as discussed above. FIG. 37( a) shows two deposition cycles including afirst precursor pulse 416 followed by a purge gas pulse 418 with zerolength delays after each pulse. FIG. 37( b) shows the correspondingchamber conductance. Each one of a plurality of low conductance periods422 (corresponding to raised shield positions) is separated from anotherby one of a plurality of high conductance periods 424 (corresponding tolowered shield positions). High conductance periods 424 occur at thebeginning and end of each purge gas pulse 418 to assist in purgingchamber 12 (FIG. 13) of resident gases.

FIG. 37( c) shows the corresponding pressure in chamber 12 (FIG. 13). Alow conductance period 422 results in a high pressure period 426. A highconductance period 424 results in a low pressure period 428. FIG. 37( c)also shows a plurality of “plasma on” periods 430 and a plurality of“plasma off” periods 432. Plasma on periods 430 occur during each highpressure period 426 during purge gas pulses 418. As discussed, the RFpower to generate plasma 194 (FIG. 13) may be synchronized with theshield position. Alternatively, the plasma can be ignited by highpressure (in the presence of the purge gas) and terminated by lowpressure, while RF bias power is constantly supplied to electrodes 80and 82 embedded in ESC 6 (FIG. 31).

Conventional ALD hardware and processes rely on the precise timing ofthe individual precursor pulses 408 and 412 and purge/pump pulses 410(FIG. 36( a)) to decrease the deposition cycle length and ensure properprocess performance. These time-based processes rely on severalassumptions including that steady state conditions exist, that all ALDreactors behave similarly, and that all gases and processes are “ontime.”

In contrast, some novel ALD process embodiments can use a state-basedapproach, rather than a time-based approach, to synchronize theindividual pulses. This can provide self-synchronization of theindividual pulses for improved process speed, control, and reliability.Instead of introducing a next gas pulse (with a fixed duration) apredetermined time after the introduction of the previous fixed durationgas pulse, subsequent gas pulses can be triggered based upon a change inthe pressure state of process chamber 12 (FIG. 13). This can beaccomplished using a pressure switch mounted in chamber body 18 capableof sensing changes in the pressure of process chamber 12. The pressurecan be modulated via the in-process tunable conductance, achieved by ashield 14 that can be moved during the deposition cycle, as describedpreviously.

FIG. 38 shows timing diagrams for another alternative embodiment of anovel ALD process. The ALD process of FIG. 38 is similar to the ALDprocess of FIG. 37, but it has an alternate plasma terminationtechnique. Accordingly, to avoid redundancy, the discussion focuses ondifferences in the embodiments.

In the ALD process of FIG. 38, shield 14 is lowered only after eachprecursor pulse 416 to assist in purging excess gaseous precursor 392and free ligands 398 from chamber 12 (see also FIG. 17 and FIG. 35( b)).The number of high conductance periods 424 in FIG. 38( b), correspondingto low pressure periods 428 in FIG. 38( c), is reduced. Thus, a lowconductance period 434 in FIG. 38( b) (corresponding to a high pressureperiod 436 in FIG. 38( c)) extends from purge gas pulse 418 into thefollowing precursor pulse 416 in FIG. 38( a). In this embodiment, theplasma is ignited by, or synchronized with, the high pressure in chamber12 (FIG. 13). Plasma on periods 430 occur during each high pressureperiod 436 during purge gas pulses 418. Plasma 194 (FIG. 13) isterminated for subsequent plasma off periods 432 (during precursorpulses 416) by a means other than pressure change, which may include,for example, disconnecting the RF power using a switch or setting the RFoutput power to zero. A switch could be located, for example, in RFimpedance matching circuit 370 or in RF power supply 380 (FIG. 32 andFIG. 33). Actuation of such a switch would be synchronized with thedeposition steps by, for example, a computer.

Novel Chemisorption Technique for ALD Processes

The chemisorption of a gaseous precursor (e.g., precursor 392 in FIG.35( a)) onto a substrate 8 may be improved by biasing substrate 8 duringfirst precursor pulse 416 (FIG. 36( b)). As discussed previously withreference to FIG. 35( a), when a molecule of gaseous precursor 392arrives at substrate 8, which is heated, a weakly bonded ligand willcleave off of the molecule, forming free ligand 398. This actuallyleaves the precursor molecule with a net charge (either positive ornegative). An opposite-polarity, low DC bias (e.g., |50V|<|V_(bias)|<0V)applied to substrate 8 will attract the charged precursor molecule tosubstrate 8 and orient it so that the desired atom is bonded tosubstrate 8 to form chemisorbed precursor 396. The lowest possible bias(e.g., |10V|<|V_(bias)|<0V) that generates a moment on the chargedprecursor molecule is desirable to correctly orient the chargedprecursor molecule with minimal charging of substrate 8.

This novel chemisorption technique for ALD processes promotes uniformand complete (i.e., saturated) chemisorption with a specifiedorientation on dielectric and metallic surfaces so that high quality,reproducible layer-by-layer growth can be achieved using ALD. The novelchemisorption technique is particularly effective for the first fewprecursor monolayers, where, in the absence of this technique, precursormolecules may chemisorb with a random orientation. This method is alsoparticularly effective in the case of organometallic precursors such asthose mentioned previously.

FIG. 39 is a schematic illustration of the novel chemisorption techniquefor ALD processes to deposit thin films, for example, for copperinterconnect technology. Two thin films used in copper interconnecttechnology are a barrier/adhesion layer and a copper seed layer. FIG.39( a) illustrates chemisorption of TaN, a typical barrier/adhesionlayer material. In the case of a precursor TBTDET 438, the Bu^(t) ligandmay cleave. A now negatively charged precursor 440 then orients with anegatively charged nitrogen 442 (e.g., the N⁻¹) toward substrate 8,which is positively biased, for chemisorption. If an NEt₂ ligand iscleaved instead, then the Ta becomes positively charged and a negativebias applied to substrate 8 would orient the Ta toward substrate 8 forchemisorption.

FIG. 39( b) illustrates chemisorption of Cupraselect® (CuhfacTMVS), atypical copper seed layer material. In the case of a precursorCuhfacTMVS 444, the TMVS ligand is cleaved. A now positively chargedprecursor 446 then orients with a positively charged copper 448 (e.g.,the Cu⁺¹) toward substrate 8, which is negatively biased, forchemisorption.

In some embodiments, the novel chemisorption technique may include anin-situ clean prior to introduction of the first precursor to promotehigh quality film deposition. As discussed above in reference to FIG.36( b), a purge gas pulse 418 (e.g., including Ar, H₂ and/or He) can beused as an in-situ clean to remove carbon-containing residues, nativeoxides, or other impurities (see, for example, Application Ser. No.60/255,812, referenced above). Removing native oxides from metal layersis especially important for low resistance and good mechanical adhesionof the film to substrate 8 (FIG. 39). H atoms can react with carbon andoxygen to form volatile species (e.g., CH_(x) and OH_(x) species). Ar⁺or He⁺ ions improve dissociation (e.g., of H₂) and add a physical clean(e.g., via sputtering by Ar⁺ ions generated in the plasma). The gasratios can be tailored to alter the physical versus chemical componentsof the in-situ clean.

FIG. 40 is a schematic diagram of a circuit 450 for electrical biasingof ESC 6 of ALD reactor 100 (FIG. 12) for the novel chemisorptiontechnique described above. The use of ESC 6 helps provide a uniform biasto substrate 8 (FIG. 39). Circuit 450 of FIG. 40 is similar to circuit372 of FIG. 32 and circuit 376 of FIG. 33. Accordingly, to avoidredundancy, the discussion will focus on differences between circuit 450and circuits 372 and 376.

In FIG. 40, with the RF power from RF generator 92 decoupled by openingan RF power switch 452, a first DC power supply 454 and a second DCpower supply 456, which are serially coupled matching supplies, performthe function of DC power supply 86 in FIGS. 32 and 33 to maintain thepotential difference between electrodes 80 and 82. This potentialdifference provides the “chucking” action that holds substrate 8 (FIG.39) to ESC 6. Serially coupled between the common node (labeled A) of DCpower supplies 454 and 456 and a ground terminal 458 are a currentsuppression resistor 460, a DC power switch 462, and a DC referencevoltage source 464. Ground terminal 458 may be the same ground referenceas ground terminal 94.

With DC power switch 462 closed, the reference voltage of electrodes 80and 82 (and therefore of substrate 8 during chemisorption as shown inFIG. 39) is established by DC reference voltage source 464. Currentsuppression resistor 460 limits the current from DC reference voltagesource 464. DC reference voltage source 464 is capable of providing apositive or negative voltage, as needed for biasing substrate 8 (FIG.39). The voltage level provided by DC reference voltage source 464 mayadditionally reduce the time required to chemisorb a complete monolayer.This may allow a reduction in the duration of first precursor pulse 416(FIG. 36( b)) and/or a reduction in the precursor partial pressureduring first precursor pulse 416.

Once chemisorption is complete, DC power switch 462 is opened to isolatevoltage source 464 and to electrically float first and second DC powersupplies 454 and 456. RF power switch 452 is closed to reconnect RFgenerator 92. The remainder of the ALD process continues as describedpreviously.

In some embodiments of ALD processes, it is possible to use a circuitsimilar to circuit 450 of FIG. 40 to generate plasma 194 above substrate8 (FIG. 13) by biasing ESC 6 using a high DC voltage (e.g., 500 V orhigher). In this case, RF generator 92, RF impedance matching circuit370, and capacitors 96 and 98 would not be used. DC reference voltagesource 464 would supply at least two distinct voltages, or switch 462would alternate between two distinct voltage sources. The first voltagewould be a low DC voltage coupled to electrodes 80 and 82 during plasmaoff periods 432 (FIG. 37). The low DC voltage might be zero volts, or anon-zero low voltage used to orient precursor molecules for improvedchemisorption as discussed above. The second voltage would be a high DCvoltage coupled to electrodes 80 and 82 during plasma on periods 430(FIG. 37) to generate plasma 194.

The novel ALD reactor is particularly suitable for thin film deposition,such as barrier layer and seed layer deposition, but the teachingsherein can be applied to many other types of reactors and many othertypes of thin films (e.g., low-k dielectrics, gate dielectrics, opticalfilms, etc.). The foregoing embodiments of the ALD reactor, and all itsconstituent parts, as well as the ALD processes disclosed herein areintended to be illustrative and not limiting of the broad principles ofthis invention. Many additional embodiments will be apparent to personsskilled in the art. The present invention includes all that fits withinthe literal and equitable scope of the appended claims.

1. A method for controlling the temperature of a substrate in an atomiclayer deposition (ALD) process chamber comprising: retaining a substrateon an electrostatic chuck assembly by electrostatic attraction, saidsubstrate, when retained by said chuck assembly, forming a backside gasvolume bounded by a backside surface of said substrate, a surface of thechuck assembly, and an annular seal; providing a single backside gasinlet into the electrostatic chuck assembly connected to a backside gassource; providing a backside gas by a first gas outlet arrangementleading to the backside gas volume for supplying said backside gas underpressure to said backside gas volume, said backside gas providing a heattransfer medium between said chuck assembly and said backside surface ofsaid substrate, the first gas outlet arrangement receiving gas from thesingle backside gas inlet; and creating a pressure gradient across anedge of said substrate by a second gas outlet arrangement, coupled tothe backside gas source, to prevent reactive gases from causingdeposition on a backside surface of said substrate or deposition on asurface of said chuck assembly, the second gas outlet arrangementcomprising a first plurality of gas openings arranged in a ringsurrounding the first gas outlet arrangement and surrounding thebackside gas volume outside of the annular seal, the second gas outletarrangement receiving gas from the single backside gas inlet, said stepof creating a pressure gradient across an edge of said substratecomprising outputting a gas from said first plurality of gas openings tocreate a pressure gradient along an edge of said substrate to reduce thepartial pressure of reactive gases along said edge.
 2. The method ofclaim 1 further comprising supplying at least one gas into said processchamber for reacting with a frontside surface of said substrate in saidatomic layer deposition process to form a layer on said frontsidesurface.
 3. The method of claim 1 wherein said first gas outletarrangement comprises a gas channel in said chuck assembly having asecond plurality of gas openings arranged in a ring within the firstplurality of gas openings, said method further comprising outputting agas from said first plurality of gas openings to create a pressuregradient along an edge of said substrate to reduce the partial pressureof reactive gases along said edge and to prevent reactive gases fromcausing deposition on a backside surface of said substrate or depositionon a surface or edge of said chuck assembly.
 4. The method of claim 1further comprising: detecting a temperature corresponding to atemperature of said substrate; and controlling a chuck assembly heater,controlling coolant flowing through a coolant channel thermally coupledto said chuck assembly, and controlling said backside gas to regulate atemperature of said substrate.
 5. The method of claim 4 wherein saiddetecting said temperature is performed by optically measuring atemperature of said backside surface of said substrate.
 6. The method ofclaim 4 wherein said detecting said temperature is performed by athermocouple that measures a temperature of said chuck assembly.
 7. Themethod of claim 4 wherein said controlling said chuck assembly heatercomprises controlling a resistive heater formed as part of said chuckassembly.
 8. The method of claim 4 wherein said controlling said chuckassembly heater comprises controlling a plasma.
 9. The method of claim 1wherein said backside gas includes one of Ar, He, and H.
 10. The methodof claim 1 wherein said backside gas provides a backside gas pressurebetween 3-20 torr.
 11. The method of claim 1 wherein said backside gasprovides a backside gas pressure between 6-10 torr.